Mosquito Repel Lore

Mosquito Repellent Lore


Are home remedies to repel mosquitoes effective ways to defend yourself from West Nile Virus?

  • Published 3 January 2005


Home remedies to repel mosquitoes are effective ways to defend yourself from West Nile Virus.

Collected via the Internet, 2003



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If we had a frog, we’d be tempted to drop it down the back of whoever wrote this. Once again inboxes have been flooded with yet another “here are easy ways to protect your loved ones” mailing. Concern about the danger of attack from mosquitoes bearing the dreaded West Nile Virus has made combating the pesky critters an even greater priority than in earlier years (when only annoyance and itchiness were at stake), making these bits of e-mailed advice more popular than ever. Many of these mailings indeed make that point openly, claiming the various proffered solutions will help “fight West Nile Virus.”

The truth is although many home remedies and oddball uses of everyday products do serve to repel mosquitoes somewhat, they don’t work very effectively for very long. If you’re worried about West Nile, douse yourself in a product that contains DEET rather than entrust your safety to used dryer sheets, VapoRub, vanilla, frogs, marigolds, or any other item touted by even your closest friends.

DEET is a chemical compound that effectively repels mosquitoes. It does not kill the critters; it just makes them unable to locate those wreathed in its essence. (Most mosquito repellents, despite the nomenclature, don’t technically “repel” mosquitoes; they block the receptors on mosquitoes’ antennae for the aspects of human beings — moisture, warmth, body odor, exhalation of carbon dioxide — which attract the critters.) DEET has been used by many millions of people worldwide for decades, and it’s considered safe when used according to directions. Some concerns have been raised about how safe it might be to use on children, so follow directions carefully when applying DEET-laced products to tykes.

According to the first study to scientifically compare a wide range of products for their effectiveness in repelling mosquitoes, most insect repellents containing herbal oils proved far less effective than those containing DEET. This study appeared in the New England Journal of Medicine in July 2002.

Mark Fradin and Jonathan Day of the University of Florida tested 17 nationally marketed mosquito repelling products under laboratory conditions. They asked 15 volunteers to stick a forearm coated with repellent into a cage containing 10 mosquitoes and observed how much time elapsed before the first bite. Products containing DEET repelled best, and the more DEET they contained, the better they worked. Off! Deep Woods, which contains 23.8 percent DEET, provided the longest-lasting protection: 302 minutes on average. By contrast, Avon Skin-So-Soft Bath Oil failed after 9.6 minutes, on average.

For decades rumor has held that Skin-So-Soft Bath Oil is an effective counter to mosquitoes, yet a 1993 Consumer Reports analysis found it ineffective for that purpose. Because so many people were buying the product for its purported mosquito combating properties, in 1994 Avon added a non-DEET repellent and a sunscreen to the popular bath oil and began marketing the new concoction as Avon Skin-So-Soft Bug Guard Repellent. Avon disputes the 2002 results posted in the New England Journal of Medicine study, claiming its Bug Guard Repellent works for three hours, not the 10.3 minutes for its Bug Guard Repellent (and the 22.9 minutes for its Bug Guard Repellent Plus) the study found, but a 2003 Consumer Reports analysis found the Skin-So-Soft repellent deterred mosquitoes for only one hour.

Folks delight in looking for homegrown solutions to various problems. Part of this urge is a need to feel in control, and part is a distrust of science, but part is also a recognition that kitchen wisdom has proved right on a number of past occasions. Besides, people love feeling they’ve been entrusted with or have stumbled upon valuable pieces of information unknown to others of their acquaintance. (We all want to feel special, after all.) Yet the desire to seek out folk remedies has at times caused folks to place their faith in the outlandish, such as the notion that burying a statuette of St. Joseph on their property will speed the sale of the land. Usually such forays into the realm of lore result in nothing worse than solutions which might not work all that well (if at all), but in the case of combating disease-bearing mosquitoes, a less-than-effective solution could prove a deadly choice. Perhaps in those halcyon days before West Nile Virus it might have seemed reasonable to take a chance on non-DEET solutions to the mosquito problem, when all that was being risked was the transient discomfort of a few bug bites, but no longer. In this instance, placing one’s faith in lore over science is a dangerous error to make.

In 2002 we saw another mosquito-related “wisdom of the inbox” piece, one which advised folks that placing bowls of water containing the dishwashing soap Lemon Joy around their yards would fell mosquitoes as they flew by. In a nutshell, no, it doesn’t work either.

Pesticides Used in Mosquito Control

There are a variety of products available on the market for the public and for professionals when it comes to mosquito control. Larvicides are chemicals designed to be applied directly to water to control mosquito larvae. Adulticides are used in fogging and spraying to control adult mosquitoes. Synergists are not toxic to the mosquitoes themselves, but they make adulticides more effective.

Some communities provide mosquito control as a service to the public and may apply pesticides from trucks or planes. To find out whether or not your community sprays for mosquitoes, try contacting your local health department or local mosquito control district.

There are several non-pesticide actions you can take. If you decide to use a pesticide for mosquito control, always remember to read and follow the label instructions carefully.

If you have questions about this, or any pesticide-related topic, please call NPIC at 1-800-858-7378 (8:00am — 12:00pm PST), or email us at [email protected]

Pesticides for Adult (flying) Mosquitoes

The following list of ingredients is not a recommendation and provides examples only.

Pesticides for Larval Mosquitoes (young mosquitoes in water)

The following list of ingredients is not a recommendation and provides examples only.

Pesticide Synergists

The following list of ingredients is not a recommendation and provides examples only.

How to Deter Mosquitoes: 7 Mosquito Repellent Tips

The top 7 ways to keep mosquitoes from crashing your party

By the DIY experts of The Family Handyman Magazine

You might also like: TBD

How to Deter Mosquitoes Overview: Uninvited guests can ruin a party!

No, we’re not talking about the crazy neighbors who live down the block. We’re talking about mosquitoes, which can turn an enjoyable outing into a swatfest. Although there’s no way to permanently eliminate mosquitoes, there are short-term solutions.

In this story, we’ll show you seven simple steps that you can take before your party to keep away most of the mosquitoes (and other annoying insects). The steps are safe and fast, and most cost just a few bucks. They’ll also help reduce the mosquito population throughout the summer.

Send Mosquitoes Packing

Try seven simple strategies to eliminate mosquitoes and enjoy outdoor entertaining.

How to Deter Mosquitoes Tip 1: Prune hedges and mow the yard to reduce shade

Reduce shady cover

Mosquitoes like shade to escape the midday heat.

Hedges, bushes and tall grass provide shade that shelters mosquitoes. They need a place to get out of the heat and sun during the day, so the fewer shaded areas they find, the less they’ll congregate in your yard.

Keep the hedges and bushes trimmed, and mow the yard at least once a week. Mow or till weedy spots to minimize shade and to keep these marginal areas from becoming overgrown jungles. Encourage your neighbors to do the same. Otherwise, you’ll just drive the mosquitoes next door—and they’ll come back often to visit.

How to Deter Mosquitoes Tip 2: Eliminate standing water

Thimbleful of water

Mosquitoes can lay eggs in tiny amounts of water.

It’s no surprise that mosquitoes are attracted to water, but it is surprising how little water it takes for mosquitoes to breed and multiply. Mosquitoes can lay eggs in just a thimbleful of water, which means that anything that holds even a tiny bit of water can be home to mosquito larvae.

Find and empty these water sources. Dispose of or drain water from old tires, buckets, unused kids’ pools, bases of flowerpots, furniture, toys, boats and trailers left outside. Keep the gutters clean so water can’t accumulate. Fill tree and stump holes with mortar. Slope ditches so they drain, and fill swampy areas with soil.

How to Deter Mosquitoes Tip 3: Treat pools of water

Chemically treat small pools

Treat pools of water you can’t drain to kill mosquito larvae.

Sometimes it’s nearly impossible to get rid of standing water. And sometimes, like when you have a small pond, you just don’t want to.

Pour a tiny amount of Agnique MMF mosquito larvicide in the water so that a thin layer covers the surface. It’ll suffocate the larvae (and any other insects in the water) without harming fish. (Buy it online at Or put Mosquito Dunk into the water. These doughnut-shaped briquettes produce a toxic bacterial spore that kills mosquito larvae, but won’t harm fish or animals. One briquette lasts for 30 days. Large bodies of water may require more briquettes. The Mosquito Dunk doesn’t repel mosquitoes; it prevents breeding. Find it at home centers in six-pack quantities. It’s also available at and other sites.

Mosquito Myth Busting

Contrary to popular opinion, these often-tried remedies won’t ward off mosquitoes:

  • Citronella candles are no more effective than other candles at keeping mosquitoes away. Candle smoke in general may have a limited effect. Likewise, planting Citrosa geraniums won’t repel mosquitoes.
  • Outdoor foggers and misting systems will temporarily reduce mosquito numbers, but they rise again as soon as the system turns off and the spray dissipates.
  • Spraying garlic will make your yard smell like an Italian dinner but does little else.
  • Bug zappers attract and kill thousands of insects, but most of them aren’t mosquitoes. They kill only a small number of mosquitoes in the area. (Ironically, they zap a lot of insects that prey on mosquitoes.)
  • Placing propane gas traps in your yard will effectively capture many mosquitoes, but again, only a small fraction of those in your yard.
  • Ultrasonic devices have no repellency value at all, according to studies.
  • Building bat towers and purple martin houses to attract potential mosquito predators has been proven useless. Bats and purple martins rarely feed on mosquitoes.

How to Deter Mosquitoes Tip 4: Stock water gardens with fish and chlorinate swimming pools

The fish solution

Goldfish or minnows will eat mosquito larvae in pools.

When water is part of your landscaping or used for recreation, you don’t want to drain it. But that doesn’t mean you have to surrender it to mosquitoes. Buy a few goldfish or minnows from a pet store or bait store and add them to your water garden. They may only live for one season, but they’ll eat mosquito larvae.

Chlorinate water that remains standing for a long period, like water in swimming pools, saunas and hot tubs. Follow the manufacturer’s recommendations for the safe use of chlorine. Keep pools covered when not in use. For small fountains, birdbaths and wading pools that you don’t want to chlorinate, simply change the water once a week to dispose of mosquito larvae. Sweep surfaces with a brush to knock off eggs before refilling the container.

How to Deter Mosquitoes Tip 5: Contact your local Mosquito Control District for large infestations

Mosquito control officials

Call your local mosquito control officials for advice and help with big infestations.

Large wooded areas, ponds and lakes are havens for mosquitoes. It’s almost impossible to treat these areas yourself, so call in the big guns—your local Mosquito Control District. Local policies vary and services are localized, but often, when the number of mosquitoes reaches a certain level, Mosquito Control will spray for them. This is also a good idea if mosquitoes are swarming your yard in unusually high numbers.

Make the call about two weeks before your party. It’ll take time for Mosquito Control to come out, conduct the test, and if needed, spray. Keep in mind that specific criteria must be met before Mosquito Control will spray private property. Your mosquito problem may not meet the threshold, but it’s worth a call.

How to Deter Mosquitoes Tip 6: Have your foliage professionally sprayed

Hire professionals

Professional exterminators will treat your yard with insecticide.

If Mosquito Control won’t spray your property, hire an exterminator to spray the foliage. This ensures a swat-free party by wiping out mosquitoes and other insects for at least a few days. Have this done one to three days before your party. Expect to pay $135 for a yard of less than half an acre and $225 for a yard up to an acre. For a (nearly) mosquito-free summer, have the foliage sprayed monthly (about $350 for the summer for a small yard).

Although you can buy sprays yourself, we recommend leaving the application of insecticides to the pros. They can buy more effective treatments that are restricted to licensed exterminators. They also know which to use and how much to apply to kill the mosquitoes without posing a hazard to other critters. When used according to the label, the insecticides pose minimal risk to humans and pets.

How to Deter Mosquitoes Tip 7: Run fans at ground level during the party

Run fans

Rapid air movement confuses the mosquitoes.

Mosquitoes are particularly attracted to body odors and the carbon dioxide we exhale when breathing. They allow mosquitoes to home in on us—and that’s when the biting starts. Dissipating these telltale human signs makes us harder to find. So, right before the guests arrive for your party, set fans on the ground and turn them on to break up the scent patterns. This simple solution is surprisingly effective for spur-of-the-moment events, when you can’t use the measures listed above.

Because of their light weight, mosquitoes are weak flyers. The breeze from the fans makes it difficult for them to fly, keeping them out of your party zone.

How to Avoid Mosquito Bites

Despite your best efforts, a few mosquitoes will probably crash your party. Follow these steps to keep them from harassing you:

  • Replace outside bulbs with yellow “bug” bulbs, which attract fewer mosquitoes than traditional lights. Find them at home centers ($2.50 for two 60-watt bulbs).
  • Apply a light coat of an insect repellent containing DEET on your skin.
  • Spray an insect repellent that contains permethrin on your clothes (not directly on your skin). Studies have shown that a combination of permethrin on your clothes and DEET on your skin effectively keeps away mosquitoes and other insects. Follow the manufacturer’s directions; overapplying can be dangerous.
  • You can outfit the whole family in clothes that have been factory treated with an insect repellent. The repellent lasts for about 25 washings. One source is ExOfficio ( Men’s T-shirts start at about $30.

Required Materials for this how to deter mosquitoes project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here’s a list.

  • Fish
  • Water treatment larvicides

What is dengue?

Dengue is fast emerging pandemic-prone viral disease in many parts of the world. Dengue flourishes in urban poor areas, suburbs and the countryside but also affects more affluent neighbourhoods in tropical and subtropical countries.

Dengue is a mosquito-borne viral infection causing a severe flu-like illness and, sometimes causing a potentially lethal complication called severe dengue. The incidence of dengue has increased 30-fold over the last 50 years. Up to 50-100 million infections are now estimated to occur annually in over 100 endemic countries, putting almost half of the world’s population at risk.

Severe dengue (previously known as dengue haemorrhagic fever) was first recognized in the 1950s during dengue epidemics in the Philippines and Thailand. Today it affects Asian and Latin American countries and has become a leading cause of hospitalization and death among children and adults in these regions.

The full life cycle of dengue fever virus involves the role of mosquito as a transmitter (or vector) and humans as the main victim and source of infection.

The virus

The dengue virus (DEN) comprises four distinct serotypes (DEN-1, DEN-2, DEN-3 and DEN-4) which belong to the genus Flavivirus, family Flaviviridae.

Distinct genotypes have been identified within each serotype, highlighting the extensive genetic variability of the dengue serotypes. Among them, “Asian” genotypes of DEN-2 and DEN-3 are frequently associated with severe disease accompanying secondary dengue infections.

The mosquito

The Aedes aegypti mosquito is the main vector that transmits the viruses that cause dengue. The viruses are passed on to humans through the bites of an infective female Aedes mosquito, which mainly acquires the virus while feeding on the blood of an infected person.

The human

Once infected, humans become the main carriers and multipliers of the virus, serving as a source of the virus for uninfected mosquitoes. The virus circulates in the blood of an infected person for 2-7 days, at approximately the same time that the person develops a fever. Patients who are already infected with the dengue virus can transmit the infection via Aedes mosquitoes after the first symptoms appear (during 4-5 days; maximum 12).

In humans recovery from infection by one dengue virus provides lifelong immunity against that particular virus serotype. However, this immunity confers only partial and transient protection against subsequent infection by the other three serotypes of the virus. Evidence points to the fact that sequential infection increases the risk of developing severe dengue. The time interval between infections and the particular viral sequence of infections may also be of importance.

How to survive the medical misinformation mess

Departments of Medicine, Health Research and Policy, and Biomedical Data Science, Stanford University School of Medicine, Stanford, CA, USA

Meta‐Research Innovation Center at Stanford (METRICS), Stanford University, Stanford, CA, USA

Department of Statistics, Stanford University School of Humanities and Sciences, Stanford, CA, USA

Correspondence to: John P. A. Ioannidis, Department of Medicine, Meta‐Research Innovation Center at Stanford and Stanford Prevention Research Center, 1265 Welch Rd, MSOB X306, Stanford CA 94305, USA. Tel.: +1 650 7045584; e‐mail:

Department of Family Medicine, University of Washington School of Medicine, Seattle, WA, USA

Delfini Group LLC, Seattle, WA, USA

Lown Institute, Brookline, MA, USA

Department of Health Policy, Harvard T.H. Chan School of Public Health, Cambridge, MA, USA

Delfini Group LLC, Seattle, WA, USA

Departments of Medicine, Health Research and Policy, and Biomedical Data Science, Stanford University School of Medicine, Stanford, CA, USA

Meta‐Research Innovation Center at Stanford (METRICS), Stanford University, Stanford, CA, USA

Department of Statistics, Stanford University School of Humanities and Sciences, Stanford, CA, USA

Correspondence to: John P. A. Ioannidis, Department of Medicine, Meta‐Research Innovation Center at Stanford and Stanford Prevention Research Center, 1265 Welch Rd, MSOB X306, Stanford CA 94305, USA. Tel.: +1 650 7045584; e‐mail:

Department of Family Medicine, University of Washington School of Medicine, Seattle, WA, USA

Delfini Group LLC, Seattle, WA, USA

Lown Institute, Brookline, MA, USA

Department of Health Policy, Harvard T.H. Chan School of Public Health, Cambridge, MA, USA

Delfini Group LLC, Seattle, WA, USA


Most physicians and other healthcare professionals are unaware of the pervasiveness of poor quality clinical evidence that contributes considerably to overuse, underuse, avoidable adverse events, missed opportunities for right care and wasted healthcare resources. The Medical Misinformation Mess comprises four key problems. First, much published medical research is not reliable or is of uncertain reliability, offers no benefit to patients, or is not useful to decision makers. Second, most healthcare professionals are not aware of this problem. Third, they also lack the skills necessary to evaluate the reliability and usefulness of medical evidence. Finally, patients and families frequently lack relevant, accurate medical evidence and skilled guidance at the time of medical decision‐making. Increasing the reliability of available, published evidence may not be an imminently reachable goal. Therefore, efforts should focus on making healthcare professionals, more sensitive to the limitations of the evidence, training them to do critical appraisal, and enhancing their communication skills so that they can effectively summarize and discuss medical evidence with patients to improve decision‐making. Similar efforts may need to target also patients, journalists, policy makers, the lay public and other healthcare stakeholders.

Currently, there are nearly approximately 17 million articles in PubMed tagged with ‘human(s)’, with >700 000 articles identified as ‘clinical trials’, and >1·8 million as ‘reviews’ (approximately 160 000 as ‘systematic reviews’). Nearly one million articles on humans are added each year 1 . Popular media also abound with medical stories and advice for patients.

Unfortunately, much of this information is unreliable or of uncertain reliability. Most clinical trials results may be misleading or not useful for patients 2, 3 . Most guidelines (which many clinicians rely on to guide treatment decisions) do not fully acknowledge the poor quality of the data on which they are based 4 . Most medical stories in mass media do not meet criteria for accuracy 5 , and many stories exaggerate benefit and minimise harms.

Clinicians and patients often do not recognise how pervasive this problem is and how profoundly it affects the care they deliver or receive. Twenty to 50 per cent of all healthcare services delivered in the United States is inappropriate, wasting resources and/or harming patients 6-10 . Much of this waste is due to overuse of medical interventions, resulting in an unknown amount of preventable harms. Underuse of effective and safe interventions further compounds the system’s failure to meet patients’ needs 11-13 . While there are many causes for inappropriate care and waste, much of it may be attributed to the poor quality of information that clinicians and patients rely on to make decisions about the services they deliver or receive.

See also:  Preventing Fleas

We use the term ‘Medical Misinformation Mess’ to encompass the set of issues that relate to the low quality of medical information deeply embedded in clinical processes and decisions. Although the Medical Misinformation Mess affects multiple stakeholders – clinicians, patients, researchers, medical information content developers (e.g. producers of guidelines and decision aids), health journalists, professional associations, policymakers, politicians, hospitals, insurers, drug companies, healthcare advocates and others – here, our focus is mainly on clinician and patient issues, and on remedies for those aspects.

The Medical Misinformation Mess comprises four key problems:

  1. Much published medical research is not reliable or is of uncertain reliability, offers no benefit to patients, or is not useful to decision makers.
  2. Most healthcare professionals are not aware of this problem.
  3. Even if they are aware of this problem, most healthcare professionals lack the skills necessary to evaluate the reliability and usefulness of medical evidence.
  4. Patients and families frequently lack relevant, accurate medical evidence and skilled guidance at the time of medical decision‐making.

Problem 1. Much published medical research is not reliable or is of uncertain reliability, offers no benefit to patients or is not useful to decision makers

With the ever‐increasing number of publications, there is a growing need for well‐designed and conducted systematic reviews and meta‐analyses to provide valid, cumulative evidence on relevant topics. This need is not easy to meet. Although systematic reviews and secondary sources may accelerate evidence uptake 14 , most systematic reviews and meta‐analyses appear to be either not useful or of uncertain utility 3 . The majority are unnecessary (duplicative), inaccurate or misleading due to biases in the methodology and selective reporting of results, or they address questions that have no clinical value.

Underlying concerns about the methodology and bias of systematic reviews and meta‐analyses is the quality of the published medical research on which they are based 2, 3 . Usefulness of clinical research 15 requires existence of a real problem to address, proper context placement, sufficient information gain, patient‐centeredness, pragmatism, reasonable value‐for‐money, nonfutility and transparency. Very few clinical studies meet at least six of the eight criteria 15 . In one survey of 60 352 studies, a meagre 7% passed criteria of high‐quality methods and clinical relevancy 16 and fewer than 5% passed a validity screening for an evidence‐based journal 17 . Uncertain or poor quality evidence leaves clinicians, often under pressure, without definitive information regarding possible treatments. For brevity, our focus here is on therapeutic interventions, but similar problems are found in publications dealing with diagnosis, prevention and other areas of medical care.

Many solutions have been proposed for making medical research more reliable 18, 19 and more useful 15 , and these will not be discussed in detail here as they have been covered elsewhere 15, 18, 19 , but this problem is unlikely to be fixed imminently. Moreover, the large amount of accumulated misleading information is difficult to extract from the literature. Meanwhile, we need to work on the other three components of the misinformation mess to prevent misleading evidence from flowing downstream into clinical decisions.

Problem 2. Most healthcare professionals are not aware of this problem

Based on training thousands of attendees at our educational programmes and professional interactions with colleagues at all levels – from young trainees to top clinical and academic leadership – we are convinced that very few healthcare professionals are aware of the pervasiveness of biased and inaccurate medical literature. It is our combined experience that ignorance of this problem, even at the highest levels of academic and clinical leadership is profound.

Evidence for this ignorance emerges also in several studies and surveys. In a study of journal reading habits, internists (approximately half of whom were alumni of the Robert Wood Johnson Clinical Scholars Program) reported they obtained information mostly from abstracts and not the full articles, stating that they relied on editors to assure rigour and study quality 20 . Such trust may be misplaced. For example, a recent study showed that several editors of peer‐reviewed journals could not tell whether a trial was randomised without a special checklist. Even then, of the 324 studies editorial staff considered as randomised trials, 127 (39%) were actually not randomised 21 .

Many healthcare professionals put too much trust in abstracts for filtering the literature, or expect that systematic reviews or guidelines will get rid of the unreliability and nonutility problem. Clearly, the reliability of a study’s results cannot be accomplished solely by reading the abstract. One study found that nearly half of abstracts of randomised controlled trials contained biased reporting of study results, implying benefit when there was no statistically significant difference in the primary endpoint between study arms 22 . Flawed primary studies are compounded by flawed systematic reviews and lead to flawed clinical guidelines that make for conflicting recommendations unsupported by reliable evidence 23, 24 . Most healthcare professionals are not even minimally aware of these issues.

Problem 3. Most healthcare professionals lack skills in being able to evaluate the reliability and usefulness of evidence

In our encounters with students, clinicians and others working in the healthcare industry (including academicians, researchers, editors, peer reviewers, pharmacists, regulators, politicians and employees of insurance companies, hospitals, the pharmaceutical industry and new technology companies), we have found a lack of the basic skills required for determining a study’s reliability and applicability. For example, in a pretest administered to a sampling of more than 500 physicians, clinical pharmacists and other healthcare professionals attending evidence‐based medicine (EBM) training programmes in 2002 and 2003, 70 per cent failed a simple three‐question critical appraisal training programme test. The three pretest questions were designed to determine if attendees could recognise the absence of a control group, understand the issue of overestimating benefit when provided with relative risk reduction information without absolute difference information and determine whether an intention‐to‐treat analysis was performed. Surprisingly, among those who reported feeling confident to evaluate the medical literature, 72 per cent failed the test, even with generous criteria for correct answers 25 . We have repeated the same pretest with various groups each year with similar results. A well‐designed and conducted trial reported similar findings: clinicians without formal EBM training score poorly on the 15‐test question Berlin Questionnaire (mean score, 4·2 correct answers compared with EBM experts’ mean score of 11·9) 26 .

Critical appraisal skills matter greatly for assuring optimal patient care. When practicing clinicians cannot distinguish between valid and false results, they are at risk of delivering useless treatments, or worse, harming their patients. For example, evidence of a fourfold increased risk of myocardial infarction in patients receiving rofecoxib (Vioxx, Merck, Whitehouse Station, NJ, USA) as compared to naproxen (Novopharm Biotech, Toronto, Canada) was plainly available in the abstract of the VIGOR trial. However, peer reviewers, editors and readers of the New England Journal of Medicine accepted the spurious argument that naproxen was cardioprotective. The VIGOR investigators concluded that the increased risk of myocardial infarction with rofecoxib did not exist, stating without any supporting evidence that the ‘…results are consistent with the theory that naproxen has a coronary protective effect’. Millions of prescriptions were written before the drug was withdrawn from the market in 2004, after several studies reported significantly increased risks of cardiovascular events and death 27 .

The potential risks of delivering poor care might be mitigated if healthcare professionals followed trustworthy clinical guidelines or based their actions on reliable systematic reviews and meta‐analyses, which ought to weed out false results. However, lack of critical appraisal skills on the part of reviewers and guideline creators routinely leads to flawed systematic reviews and guidelines, leaving clinicians with few resources for sorting fact from fiction 3 .

The teaching of appraisal skills in medical and other schools and other training programmes, such as residencies, appears at first glance to be fertile ground for providing clinicians with needed skills. However, studies assessing medical student competencies suggest they frequently do not see or are not taught the relevance of EBM to clinical care and are neither motivated nor prepared to apply EBM skills. Upon entry to residency programmes, their ability to appraise the medical literature critically is extremely limited 28 .

Currently, strong evidence regarding the most effective training approach to equip healthcare professionals with the required knowledge and skills to consistently apply valid research evidence in their daily work is lacking. Studies of the effectiveness of teaching EBM and critical appraisal of medical evidence are heterogeneous in study designs, populations, intervention components, outcome measures, study settings, duration and other factors. Several systematic reviews have reported that teaching EBM is effective, but study details and methodological quality vary widely 29-31 . An overview of reviews 29 found 16 systematic reviews that have tried to cover this topic and more reviews were published since then 31 . Most systematic reviews have concluded in favour of the effectiveness of EBM teaching, but outcomes vary and focus mostly on knowledge and skills rather than practical applications, while randomised trials are relatively few. For example, a Cochrane review of EBM teaching effectiveness 32 concluded that EBM teaching does have positive impact on the knowledge and skills of physicians. This is based on only three RCTs 33-35 (with total sample size n = 270, shown along with risk of bias assessments 36 in Table 1) meeting the investigators’ criteria after reviewing a total of 11 057 titles and abstracts yielding 148 potentially relevant studies. Another systematic review 31 of teaching EBM in healthcare professionals excluding physicians and medical students found only 13 eligible studies with a total of 1120 participants and of those only four (with 168 participants) were randomised. The durability of the effects and the optimal ways of maintaining acquired knowledge and skills are even less studied.

Unclear risk of bias

Small trial lacking in details of randomisation and concealment of allocation; minimal loss to follow‐up; assessors were blinded.

Knowledge: validated tool – 18 multiple‐choice questions focused on knowledge of principles for appraising evidence.

Skills assessment: appraisal of a systematic review.

Knowledge score: mean difference 2·6 (95% CI: 0·6–4·6).

Skills assessment: mean difference: 1·2 (95% CI: 0·01–2·4).

Unclear risk of bias

Computer generated randomisation codes; unclear concealment of allocation; balanced groups; attrition incompletely reported; adequate blinding of assessors.

  • a Risk of bias ratings based on Cochrane Collaboration’s ‘Risk of bias’ assessment tool 36 that examines the following six criteria: sequence generation, allocation concealment, blinding of participants, personnel and outcome assessors, incomplete outcome data, selective outcome reporting and other sources of bias.

Problem 4. Patients and families frequently lack relevant, accurate medical evidence and skilled guidance at the time of medical decision‐making

People are bombarded with medical news stories, television and radio talk shows, social media, pop culture magazines, spurious websites, direct‐to‐consumer drug and medical device ads, hospital marketing messages and other media sources, much of which are incomplete or wildly inaccurate 37 . Some television shows hosted by physicians amount to hucksterism. Today, more media articles have begun to note problems in medical science: instances of biased medical research, a lack of evidence for both alternative and allopathic treatments and the problem of conflict of interest. But many health care and medical journalists appear to remain largely unaware of the degree to which the ‘information’ they gather for stories has been shaped by the interests of manufacturers and research universities. Mass media consumers have few means of determining the accuracy of any given news item and thus often view evidence through the lens of the mass media. We need to educate the public how to deal with these sources of misinformation 38-40 .

Informed or misinformed, patients eventually are at the core of making medical decisions 41 . The legal doctrine of informed consent requires that patients understand that they have treatment choices and the potential benefits and harms of each choice 42 , while medical ethics recognises that their values and preferences must be honoured 41 . Shared decision‐making (SDM) involves clinicians sharing medical evidence with patients, eliciting their values and preferences and deciding with their patients the best course of treatment. Ensuring that patients are adequately prepared to make decisions usually requires professional assistance to explore both the treatment options and the medical evidence, so that the potential outcomes that matter most to the patient can be accurately determined. This process depends on sufficient, relevant and valid information, and clarifying discussion that confers ‘agency’ – the capacity of an individual to make free choices 43, 44 .

Use of SDM and decision support materials (often called patient decision aids) improves decision‐making around many different ‘preference‐sensitive’ clinical choices. A systematic review of 115 randomised controlled trials involving more than 34 000 patients of the effects of SDM and exposure to decision aids (written, electronic, audiovisual or in web‐based tool formats), reported that patients had greater knowledge gain, felt more confident regarding what mattered to them and had more accurate expectations about risks and benefits than patients who received usual care. Participants in the experimental arms participated more actively in the decision‐making process and were on average

20% more likely to make conservative choices when facing difficult decisions regarding surgical and nonsurgical interventions, resulting in no known adverse health outcomes, decreased satisfaction or anxiety 45 .

Given the power of patient decision aids and clinician–patient dialogue, both need to be accurate if patients are to make properly informed decisions. Accuracy of decision aids depends upon the critical appraisal skills of their producers 46 , while the effectiveness of clinician–patient conversations requires clinicians who are willing and able to engage and know the evidence. Barriers to implementing effective SDM include pervasive professional indifference, organisational inertia, lack of physician comfort with decision aids, time constraints, competing priorities, lack of training, lack of reimbursement and perceived work burden and cost 47 . Patients’ preferences for a treatment often differ from those of clinicians 48, 49 , yet clinicians often underestimate patients’ desires for information 50 .

Not surprisingly, discussions with patients infrequently fulfil the criteria considered integral to informed decision‐making and informed consent. A study of outpatient visits in primary care clinics assessed six elements of informed decision‐making: description of the nature of the decision, discussion of alternatives; discussion of risks and benefits, discussion of related uncertainties; assessment of the patient’s understanding and elicitation of the patient’s preference. No discussions fulfilled all criteria. Physicians frequently described the nature of the decision (83%), but infrequently elicited patients’ preferences (19%), discussed alternatives (14%), risks and benefits (9%), uncertainties (5%) and rarely (2%) assessed the patient’s understanding of the decision 51 . In a similar study, only rarely (1·1–16·6%) did physicians relate to patients the uncertainty of evidence surrounding the recommended treatments 52 .

The combination of unreliable medical evidence, the tsunami of misleading reports in the media, inadequate discussions between clinicians and patients and a culture of patients’ trust in providers’ recommendations and expectation of something to be done together produce massive medical misinformation, with suboptimal, nonpatient‐centred decision‐making.

Moving forward

We think that all healthcare professionals involved in medical decision‐making should possess basic critical appraisal skills and be knowledgeable about which sources of information are likely to be accurate and relevant. As Glasziou et al. 53 have stated, ‘a 21st century clinician who cannot critically read a study is as unprepared as one who cannot take a blood pressure or examine the cardiovascular system’. Such illiteracy is common and clinicians thus foster unrealistic expectations about medicine. A systematic review of 48 studies on clinician expectations on the benefits and/or harms of treatments, tests or screening tests showed that in most studies most physicians had inaccurate expectations. Moreover, it was far more common for clinicians to overestimate than underestimate benefits and to underestimate rather than overestimate harms 54 . Their inability to assess evidence further contributes to skewed views among patients, the media, policy makers and others.

The problem of having so much unreliable and nonuseful published medical research may be attacked at its root, that is by funding, conducting, publishing and disseminating more true and useful research. However, it is important in the meantime to make healthcare professionals, patients, journalists and others aware of the problem, provide them with critical appraisal skills and ensure that the best evidence available is included in clinician–patient discussions about treatment choices.

How to accomplish those three goals is neither obvious nor simple. We need additional high‐quality RCTs on the effectiveness of specific interventions to teach EBM. Assessed interventions may include both fixed components (e.g. basic EBM concepts and skills) and variable components (e.g. contextual elements such as settings, leadership support, involvement of opinion leaders and other details regarding employed implementation strategies) 55 . It has not been decisively shown which implementation strategies are optimal for a given clinical practice change. Important barriers and considerations for successful clinical practice change may include personal factors (e.g. motivation, time, skills required to evaluate the relevance and validity of medical information), recommendation‐related factors (access, complexity) and external factors (e.g. local clinical culture) 56 .

We should also caution that any of the EBM critical appraisal tools can be subverted. For example, industry‐sponsored trials may be performed and presented in a way that they tick all the boxes in the CONSORT checklist and on risk of bias tools, even as some fundamental aspects of their design, for example the question asked and how it is asked and answered (what comparators, outcomes or follow‐up are used), may still be highly misleading. There is no standard package or automated training tool to substitute for thinking and some healthy scepticism. Similarly, while decision tools can enhance SDM, automated tools alone cannot address some additional fundamental challenges that weaken the position and involvement of patients in the decision‐making. For example, patients typically have had little or no input to the design of the research that produced the available evidence, power imbalances may exist in the clinical consultation, and many people do not seek or cannot access care 57 . In addition, journalists must be trained to bring greater scepticism and some critical appraisal skills to reporting on medical research. Addressing these challenges requires rethinking medical research and care at large.

Acknowledging these broader challenges, agents of change could include journals, government agencies, professional groups, schools for healthcare professionals, payers, accreditation bodies, as well as fellow healthcare providers who can reinforce the importance of mastering critical appraisal and communication skills in every day’s practice. The mass media have a special role to play in this regard, as all players in healthcare, from journals to clinicians to government agencies, may respond to criticism in the press.

Critical appraisal skills may have a short half‐life and need continuous use and reinforcement. Moreover, given the vast and rapidly expanding nature of the literature and the limited time available to healthcare professionals, it may be easier to focus on using critically pre‐appraised evidence, for example from well‐done evidence synthesis efforts or guidelines, rather than try to appraise every single article. However, even systematic reviews, meta‐analyses and guidelines are currently so numerous and often so poor, biased, conflicted or useless that building and maintaining skills to appraise them is not an easy task. Moreover, becoming proficient in dissecting the caveats of higher‐level syntheses requires understanding the problems of primary studies.

As more journal editors recognise the Medical Misinformation Mess as an issue, they can promote awareness by publishing articles, commentaries and editorials on the subject. It seems astonishing that there is a need to point out that investigators should understand what constitutes good design, methodology, execution, performance and reporting in research; nevertheless, the need exists. Journals should require manuscripts to provide all information required for their critical appraisal. Government agencies and professional groups may also be influential stakeholders in ensuring that investigators possess key EBM skills. The press also needs training in critical thinking 58 . Schools of journalism should include basic epidemiology and statistics in their coursework for future healthcare and medical writers. Journalists and editors should also be aware of the evidence‐based critiques of mass media stories, such as those offered by 38 .

Schools for healthcare professionals could do a better job of ensuring that training in critical appraisal of the medical literature is integrated into the curricula and clinical care. Encouraging reports suggest that attitudes, knowledge and critical appraisal skills can improve through tightly integrated EBM teaching programmes 59, 60 . Payers and accreditation bodies, such as the Accreditation Council for Graduate Medical Education, involved in the delivery of healthcare, could also require skills in critical appraisal of medical evidence.

Eventually, successful initiatives should be part of everyday clinical experience, not seen as an artificial formal imposed requirement. Teachers and trainers need ever sharper skills in critical appraisal of the medical literature 59 . Furthermore, all healthcare professionals can take up the responsibility to master skills and become teachers and trainers for themselves and for others during encounters with patients and decision‐making.


METRICS is funded by a grant from the Laura and John Arnold Foundation. The work of John Ioannidis is supported by an unrestricted gift from Sue and Bob O’Donnell.

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Reference Study design/size/population Intervention Outcomes Effect size Risk of biasa a Risk of bias ratings based on Cochrane Collaboration’s ‘Risk of bias’ assessment tool 36 that examines the following six criteria: sequence generation, allocation concealment, blinding of participants, personnel and outcome assessors, incomplete outcome data, selective outcome reporting and other sources of bias.
Linzer et al. 33 44 internal medicine interns at Duke University who volunteered General medicine journal club that emphasised epidemiologic methods and critical appraisal of medical evidence; five journal club sessions (mean); conducted over average of 9·5 months led by general medicine faculty; control group received seminars dealing with ambulatory medicine issues. Per cent improvement in knowledge using a test instrument developed by the Delphi method. 26% improvement in the intervention group compared with 6% improvement in the control group (P = 0·02).
MacRae et al. 34 81 members of the Canadian Association of General Surgeons who volunteered for 6‐month Internet‐based study; included surgeons from most provinces. Internet curriculum in critical appraisal skills; included a clinical and methodologic article, a listserve discussion of methodology; methodologic critiques; 16 articles assessed with critical appraisal guide; control group received articles to read and had access to online critical appraisal articles. Primary outcome measure: locally developed 51 item test to assess validity assessment and applicability skills. Intervention group score on examination: 58·8% vs. control group score of 50% (P 20%; adequate blinding of assessors.

Taylor et al. 35 145 self‐selected general practitioners, hospital physicians, allied health professionals, healthcare managers/administrators from the south‐west of England. Half‐day skills training based on the Critical Appraisal Skills Programme (CASP) developed from educational methods of McMaster University; control group: waiting list for workshop.