Why do we need evidence-based medicine?

You may find the following information useful to share with patients who would like to understand more about EBM and weighing the different information sources. You may also find some ideas on how to discuss EBM and making informed decisions with your patients.

When researchers study a disease or a condition, they usually look at many more patients than any one doctor will ever treat. Also, medical knowledge changes all the time. And what doctors used to think was the best thing to do, even a few years ago, might actually be considered harmful today.

Only by looking at all the evidence and judging it fairly can you work out what the research really says about a medical test or intervention, and how this relates to you as an individual. This is called evidence-based medicine.

Key points about evidence-based medicine

• Evidence-based medicine looks at all the research that there is about a disease or treatment.
• However, all evidence is not alike. Some evidence is better than other evidence. (See “How to weigh sources of information” below)
• The evidence alone can't tell you which treatment is best for you, so it's important that you weigh the benefits and harms of treatments carefully along with your own values and preferences.

Why evidence from research is so important

Information or advice from family and friends, or from the internet, however well intentioned, may be unhelpful or even harmful. For example, just because a cancer drug worked for one person doesn't mean it will work for you. Also, there have been many practices in medicine that were later found to be useless or even harmful when studies were done. For example, resting in bed used to be recommended for many conditions. But now we know that it can often do more harm than good. People who have had a heart attack, for example, do better both physically and mentally if they begin exercising as soon as they feel well enough.[1]

How to weigh sources of information

What friends and family say
When you are sick, your family and friends often give you advice and tell you about their experiences. These stories can be very powerful. If your mother says that your son needs to have his tonsils taken out because he has had so many sore throats, you may believe what she says because she is your mom. She may say that, when you had your tonsils out, you stopped missing school and started eating better and growing more.

But research shows that removing children's tonsils may not do them much good, and after a year or two they may have as many sore throats as children who didn't have their tonsils out.[2] And some children get complications from tonsil surgery, such as bleeding. Your mom means well, but one person's story is just that: it is the story of one person who had a treatment. It is not the story of thousands of others who also have had it.

For example, you often hear stories of people who have survived cancer because they went on strict diets. However, you are less likely to hear about people who went on strict diets and died. They are not around to tell their stories. It can be hard to follow a strict diet if you have cancer and find eating difficult. It may keep you from enjoying your life. You should think carefully before you start a diet that is difficult and unpleasant to follow, and do it only if research shows that you will get some real benefits from it.

However, you can still learn a lot from one person's experience of treatment. Research studies do not always look at the things that matter to you. What friends and neighbors and other people with your condition say is important. But you shouldn't use this information on its own when you make decisions about treatment.

What your doctor says
Ideally, your doctor's treatment recommendations will be based on the most reliable research available (often this would be large clinical trials). But it's tough for busy health professionals to keep up to date with advances in medical knowledge and the very large amount of published studies.

Evidence-based guidelines (international, national, or local) and systematic reviews (summaries of the available evidence for a particular medical question) make it a bit easier for doctors to keep up to date. However, the research doesn't always provide a clear answer on what treatment works best, so different doctors may come to different conclusions.  You can ask your doctor what evidence they have considered when giving you advice.

What the media say
Every day there are stories in newspapers or on television about the latest discoveries in health care. One day you may hear that drinking alcohol can lower your chance of heart disease. The next day you may hear that it can increase your risk of breast cancer. What should you do?

The media often report on the results of just one study. There may have been other studies that had different results, and the reporter may not know about these. Usually, any one study just adds a brick into a growing wall of evidence. The results of one study cannot tell you the whole story. It is only after other groups of researchers repeat the study and find the same results that answers become reliable.

You do not need to make a decision on the basis of one study.

The media also tend to be optimistic about advances in medicine. For example, a study that looked at how the media reported on drug treatments for osteoporosis and high cholesterol found that the benefits of the drugs were stressed but the possible harms were barely mentioned.

There are also a lot of websites that provide health information. But it can be hard to know which ones to trust.

What tradition says
Just because something has been used for years doesn't mean it works or can't hurt you. Many complementary and alternative medicines (such as herbal products and vitamins) have been used for years. But there isn't always good evidence that they do more good than harm.

One study looked at seven reference books.[3] It found that more than 100 different complementary medicines were recommended for asthma. But there was no good evidence that they worked.

Traditional remedies may have been used for centuries, but they may not be safe when taken with modern medicines. St. John's wort, for example, is a herbal remedy for depression. Unfortunately, it stops some drugs, such as the birth control pill and blood-thinning pills, from working properly.

Useful Questions
Here are some questions that might help you weigh the information you find in the media or on the internet about treatments. You may want to discuss these with your doctor.

• How could this treatment help me? Has it been studied in people like me?
• Is it likely that this drug will harm me? Am I more likely to get side effects than other people? (For example, older people sometimes have more side effects.)
• How strong is the evidence that this treatment works? Are the results of the research published in a medical journal? Is just one person telling their story on television?
• What are the alternatives to the treatment being offered?
• What are the costs of the treatment? (These can include financial and nonfinancial costs, such as inconvenience.)

Content created by BMJ Knowledge Centre

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References

1. National Institute for Health and Care Excellence. Myocardial infarction: cardiac rehabilitation and prevention of further cardiovascular disease. November 2013. Available at https://www.nice.org.uk/guidance/cg172 
2. Paradise JL, Bluestone CD, Bachman RZ, et al. Efficacy of tonsillectomy for recurrent throat infection in severely affected children: results of parallel randomized and nonrandomized clinical trials. New England Journal of Medicine. 1984; 310: 674-683
3. Ernst E, Berman B, et al. The desktop guide to complementary and alternative medicine: an evidence based approach. Mosby, Edinburgh, UK; 2001.