Why do we need evidence-based medicine?

In the past, doctors didn't always have access to the latest medical research. They often decided how to treat patients using only their own judgement and experience and what they learned at medical school. We now know that this is not the best way to practise medicine. This is because what doctors think is best for a patient is not always what the research shows is best.

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 treatment. This is called practising evidence-based medicine.[1]

Key points about evidence-based medicine

• All evidence is not alike. Some evidence is better than other evidence.
• When doctors look at the research before recommending a treatment, they are using evidence-based medicine.
• Evidence-based medicine looks at all the research that there is about a disease or treatment.
• When researchers look at whether a treatment works, they look at many more patients than a single doctor will ever treat.
• Sometimes the evidence can't tell you which treatment is best for you, so it's important that you weigh up the benefits and harms of treatments carefully.

Why evidence from research is so important

All evidence is not alike. It can be dangerous to rely on what your neighbours or friends tell you. For example, just because a cancer drug worked for them, that doesn't mean it will work for you. Also, there have been many practises in medicine that were later found to be useless or even harmful when studies were done.

Here are some examples:

• Fifty years ago, women were often given an enema while they were in labour. This is uncomfortable and unpleasant. But doctors thought that enemas would reduce the risk of infection for the woman and her baby. Some hospitals gave soapy enemas, which were painful for women. When doctors studied the results from the research they found there was no evidence that enemas prevented infections. Two studies showed that enemas made more of a mess, and women felt embarrassed by the enema.[2] Women no longer have enemas while they're in labour.
• 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.[3]

Sometimes research has proved that a treatment works, but doctors have been slow to start using the treatment. For instance, tens of thousands of premature babies died because a treatment that could help them breathe better was not widely used. In 1972, the first of several studies was published showing that giving drugs (called corticosteroids) to women about to have a premature baby could help the baby's breathing.[4] But it was another 20 years before obstetricians (doctors who specialise in pregnancy and childbirth) began using these drugs regularly.

How to weigh other sorts of evidence

What friends and family say
When you aren't well, 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 mum. 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.[5] And some children get complications from tonsil surgery, such as bleeding. Your mum 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 neighbours 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. But it's tough for busy health professionals to keep up to date with advances in medical knowledge. A 1992 study found that a doctor would have to read 17 articles in medical journals every day of the year to keep up with new information in their area of medicine.[6] This number could be even higher today.

However, more medical information is now summarised to make it easier for doctors to keep up to date. Even so, not all doctors use this type of information. Also, the research doesn't always provide a clear answer on what treatment works best, so different doctors will come to different conclusions. For men with prostate cancer, for example, some doctors recommend surgery, others recommend radiotherapy, and others think some men will do just as well without any treatment.[7]

What the experts say
Your doctor may be an expert in their field. Or your doctor may decide how to treat you based on what other experts say. Much of what doctors learn at medical school is based on what experts think. Doctors like to ask their colleagues for advice.

But experts don't always get it right. It is safer to rely on the results of good research studies than on one person's opinion.

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.[8] 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 contraceptive pill and blood-thinning tablets, from working properly.

Questions to ask your doctor
Here are some questions that might help you weigh up the information you find in the media or on the Internet about treatments. You could show these questions to 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 non-financial costs, such as inconvenience.)

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References

1. Sackett DL, Rosenberg WM, Gray JA. Evidence based medicine: what it is and what it isn't. BMJ. 1996; 312: 71-72.
2. Cuervo LG, Rodriguez MN, Delgado MB. Enemas during labor (Cochrane review). In: The Cochrane Library, Issue 2, 2000. Update Software, Oxford, UK.
3. 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 (last accessed on 8th February 2019)
4. Liggins GC, Howie RN. A controlled trial of antepartum glucocorticoid treatment for prevention of the respiratory distress syndrome in premature infants. Pediatrics. 1972; 50: 515-525.
5. 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
6. Davidoff F, Haynes B, et al. Evidence based medicine. BMJ. 1995; 310: 1085-1086.
7. Yamey G, Wilkes M. Prostate cancer screening: is it worth the pain? San Francisco Chronicle. January 18, 2002: 29.
8. Ernst E, Berman B, et al. The desktop guide to complementary and alternative medicine: an evidence based approach. Mosby, Edinburgh, UK; 2001.