There are more than 30,000 medical journals and hundreds of thousands of research articles published every year. How can anyone keep up with them? And more importantly how can you tell if the research is good or not? Each research study is only one piece of a jigsaw that may take years to finish. Rarely does any one piece of research answer either a doctor's, or a patient's, questions.

Our information is based on Clinical Evidence, a publication written for doctors by experts from all over the world. These experts look at all the research evidence on how to treat a medical condition. They carefully weigh it up and decide which treatments work and which don't work. They include research studies that have been published and also those that haven't been published.

Clinical Evidence is published by the British Medical Journal, which has been publishing information for doctors since 1840.

As new studies are published, Clinical Evidence is updated. And the results of these new studies are evaluated regularly. We provide you with the same high standard of information as you find in Clinical Evidence. So you can see the information that doctors use to make decisions about treatment.

Key points to remember about looking at studies

  • Sometimes doctors introduce new treatments too quickly, before they have been shown to work.

  • And sometimes they are too slow to use new treatments that have been shown to work.

  • Doctors and other health professionals are not always as good as we might think at deciding what is good research.

  • You need to be sure that the advice you get on health or treatments comes from high-quality studies whenever possible.

  • Two of the best sorts of research are called systematic reviews and randomised controlled trials.

When you read our information, you'll see numbers at the end of some sentences and at the bottom of some pages. These numbers are reference numbers. They tell you where you can find the research evidence that backs up what we're saying.

Some of the titles of the research articles might sound complicated. That's because they're written for doctors.

The information in this section will help you answer the following questions:

  • What are the different types of studies?

  • How can I find reliable studies?

  • How can I use research to make decisions?

What are the different types of studies?

There are different types of studies, and they don't all give you reliable information that can help in making decisions. There are three main types of studies that can help you decide whether a treatment works:

  • Randomised controlled trials

  • Systematic reviews

  • Observational studies.

It's not easy to explain these studies in one sentence, so we've used examples to show what they are.

Randomised controlled trials

In this type of study, patients are randomly assigned to have either the treatment being tested or a comparison treatment (sometimes called the control treatment). Random really means random. The decision to put someone into one group or another is made like tossing a coin: heads they go into one group, tails they go into the other. (Randomised controlled trials are sometimes called RCTs for short.)

The control treatment might be a different type of treatment or a dummy treatment that shouldn't have any effect (a placebo). Researchers then compare the effects of the different treatments.

Ideally, neither the researchers nor the patients know which treatment a patient is being given until the end of the study. They shouldn't find out until all the results have been worked out.

Making sure that no one knows what group a person is in is called 'blinding'. Blinding is a way of reducing the effect that people's expectations have on the results of a study. It is important because if researchers or patients expect a treatment will have a certain effect, then that effect is more likely to occur or be recorded. (A good example of this is that some patients taking placebo tablets also report harms or benefits, even though these tablets have no active ingredients. This is known as the placebo effect.)

However, sometimes it's not possible to hide what treatment is being used. In a study comparing plaster casts with bandages for leg injuries, for example, it would be obvious what treatment a patient was receiving.

Randomised controlled trials are used to answer questions. For example: Does a steroid cream help clear up eczema? The best way to see whether this cream works is to randomly pick which people use the cream and which do not. This means that each person in the study is randomly assigned to either the steroid-cream group or the control group. In this example, the control group would use a cream that doesn't contain any active ingredients (a placebo cream). The people using the steroid cream should be similar to those using the placebo cream (for example, they should have similar amounts of eczema).

After the people have been divided into groups, the researchers then monitor them to see how their eczema changes during the study. If the steroid cream works, people using this cream should have more improvement in their symptoms than those using the placebo cream.

When studies are not randomised (with people put into different groups randomly), controlled (with one group given a placebo or comparison treatment) and blinded (where no one knows what group someone is in), they may exaggerate how good a treatment is.

Systematic reviews of randomised trials

Often a single randomised controlled trial doesn't tell us enough about a treatment. The best answers are sometimes found by combining the results of many randomised controlled trials.

A systematic review is a type of study that looks at the results from all of the good-quality randomised controlled trials on a topic. It adds together the results of these individual studies into one summary. This gives an estimate of a treatment's risks and benefits. Sometimes these reviews include a statistical analysis, called a meta-analysis, which adds up the results of several studies.

Here is an example of why systematic reviews are useful.

  • Each year, tens of thousands of deaths are prevented all over the world because people who have had a heart attack start taking aspirin. But one randomised controlled trial suggested this treatment was not helpful, even though other good studies said it was.[1]

  • Even when randomised controlled trials are done well, they can sometimes come up with different results. This can happen because the researchers may not have taken account of things that could affect the results. And sometimes the results are different just by chance.

  • A meta-analysis was done to look at the results of all the studies of whether aspirin was helpful for people who'd had a heart attack. It found that aspirin does reduce the risk of a person dying earlier, having another heart attack, or having a stroke.[2]

An international organisation called the Cochrane Collaboration, named after a well-known researcher, does some of the highest-quality systematic reviews.

Systematic reviews are not foolproof. Their findings are only as good as the studies that they include. But the best reviews clearly state whether the studies they include are good quality or not.

Observational studies

Large randomised controlled trials are expensive and take time. And sometimes it would not be ethical to do a study in which some people were randomly assigned not to have a treatment. For example, it wouldn't be right to give oxygen to some children having an asthma attack and not give it to others. In cases like this, an observational study may be the best choice.

In an observational study, researchers observe groups of people instead of randomly dividing them into treatment groups. Although these studies are cheaper and faster than randomised controlled trials, their results are not as reliable. They cannot show cause and effect. This means they can't prove that something caused something else.

For example, one observational study spotted what seemed to be a benefit from the antioxidant known as beta-carotene, which is found in carrots.[3] Researchers noticed that people with higher levels of beta-carotene in their blood were less likely to have cancer and heart disease. So some doctors thought that beta-carotene might be responsible for keeping them from getting these diseases.

To find out if beta-carotene really did prevent cancer and heart disease, doctors needed to do a randomised controlled trial. The observational study wasn't good enough to answer the question: "Does beta-carotene help prevent cancer and heart disease?"

When the better-quality study was done (people were randomly given either beta-carotene or placebo tablets) beta-carotene didn't work. In fact, the study suggested that beta-carotene might even increase the risk of cancer.[4]

Laboratory studies

Laboratory studies are another type of study. Newspapers often have stories of studies showing how a drug cured cancer in mice. But just because a treatment works for animals in laboratory experiments, this doesn't mean it will work for humans. In fact, most drugs that have been shown to cure cancer in mice do not work for people.

What if there are no studies?

Doctors can't always base their treatment decisions on the results of studies. Sometimes the research hasn't been done because doctors are used to treating a condition in a way that seems to work. This is often true of treatments for broken bones and operations. But just because there's no research for a treatment doesn't mean it doesn't work. It just means that no one can say for sure.

How can I find reliable studies?

Our information is based on the best available research. You can find details on these studies at the end of each section. There, we list where each study was published and when, often with a link to a summary of the study (called an abstract).

You can also read entire studies in medical journals. This information is written for doctors, and some of it may be difficult to understand. A medical dictionary can help.

The main medical journals that many doctors look at are:

Some of the systematic reviews done by the Cochrane Collaboration ( are written for patients. And there is a section on how to make sense of research.

How can I use research to make decisions?

You can use our information to help you make decisions. If you are deciding whether to have surgery on your knee for osteoarthritis, for example, our information can help you discuss this with your doctor. You will also need to consider your own needs and preferences when making your decision. You may, for example, want to avoid surgery and try physiotherapy. Or perhaps your pain is severe andstopping you from being independent. If this is the case, you may want to have surgery so you can get around more easily.

Often there is more than one way to treat a condition, and the research may not be able to tell you which treatment is best. It certainly can't tell you which treatment is best for you. Only you can decide if a side effect is worth putting up with or if you can face the risk of something going wrong.

What our information can do is make it easier to talk to your doctor. This is because we provide you with the best evidence from the research – the same information doctors use to judge treatments.

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