Consumer Reports Health.org is based on information from Clinical Evidence, a book and online resource written for doctors by experts from all over the world. These experts look at all the evidence for a treatment. They weigh it carefully 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. This is what evidence-based medicine is: a way of looking at and valuing all of the research about a condition and its treatment. The experts also look at the side effects of treatments.As new studies are published, the Clinical Evidence team updates its listing of studies. And the results of these new studies are evaluated regularly.

• Sometimes health professionals introduce new treatments too quickly, before they have been shown to work.
• And sometimes they are too slow to adopt new treatments that have been shown to work.
• Health professionals are not always as good as we might think at figuring out what is good research.
• You need to be sure that the advice that you get on health or treatments comes from high-quality studies whenever possible.
• You can be more confident that you have an accurate picture of how the benefits and harms of a treatment stack up if your information comes from a systematic review or a randomized controlled trial.

Clinical Evidence is published by the BMJ Publishing Group, an independent company that has been publishing information for doctors for 160 years. It is based in the United Kingdom, but one-third of its expert researchers and editors are from the United States.Consumer Reports Health.org provides you with the same high standard of information as you find in Clinical Evidence. So you can see the information that your doctor uses to make decisions about your treatment.Not all information from research studies is accurate. That's why Clinical Evidence sifts through all the studies about a treatment to find the best ones.When you look at our Web site, 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. But a librarian should be able to help you find the reference.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?

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

• Randomized controlled trials
• Systematic reviews
• Observational studies.

It's not easy to explain them in one sentence, so we've used examples to show what they are. This is a type of research study in which patients are randomly assigned to have either the treatment being tested or a dummy 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. (Randomized controlled trials are sometimes called RCTs for short.)When the treatment being tested is a drug, this dummy treatment is sometimes a pill without any active ingredients. This type of treatment is called a placebo treatment. The placebo shouldn't have any effect at all. Sometimes one treatment is compared with another. Neither the researchers nor the patients know which treatment the patients have been given until the end of the trial. They shouldn't find out until all the results have been studied. Randomly assigning people to the different groups reduces the risk that researchers or patients will respond better (or worse) to a new treatment simply because they expect that they should respond a certain way. This problem is known as bias.Randomized controlled trials are used to answer questions. An example of a question asked by a randomized controlled trial would be: Should women who have been through menopause take hormone replacement therapy to reduce the risk of having a heart attack?The only way to see whether hormone replacement therapy (also called HRT) makes a difference is to randomly pick which women get the drug and which do not. This means that each woman in the study is randomly assigned to either the HRT group or to what researchers call the "control" group. All the women in the control group take a dummy pill. Dividing the women into groups is a way of making sure that the groups have a similar mix of women. The group of women taking the active treatment should be similar to the group of women who are taking the dummy treatment. After the women have been divided into groups, the researchers follow them up to see how many women in each group have a heart attack. It is important that neither patients nor researchers know who is having an active treatment and who is having a dummy treatment. Making sure that no one knows what group a woman 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 patients or their doctors expect a treatment to have a certain effect, that effect is more likely to occur or to be recorded. (A good example of this is that some patients taking placebo pills that have no active ingredients also report harms or benefits. This is known as the placebo effect.) Studies that are not randomized (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) tend to exaggerate how good a treatment is.In the example of HRT, it turns out that there are no research studies that are randomized, blinded and placebo-controlled in women who do not have heart disease.There is a study in women who had already had coronary artery disease.¹ It did not find that HRT reduced the risk of having a heart attack. For women who do not have heart disease, there is no good quality evidence to show that using HRT for a long time will reduce their risk of dying from heart disease or having a heart attack. Sometimes a single randomized controlled trial doesn't really give us enough information about a treatment. The best answer is sometimes found by combining the results of many randomized controlled trials.A systematic review is a type of study that looks at the results from all of the good quality randomized controlled trials on a topic. It pools the results of these individual studies into one summary. This provides an estimate of a treatment's benefits and harms. (Sometimes these reviews include a statistical analysis, called a meta-analysis, that 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 randomized controlled trial suggested this treatment was not helpful, even though other good studies said it was.²
• Even when randomized 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. (These things are called biases.) 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. It found that aspirin does reduce the risk of a person dying, having another heart attack or having a stroke.³

An international organization called the Cochrane Collaboration, named after a well-known researcher, produces some of the highest quality systematic reviews.Systematic reviews are not foolproof. Their quality is only as good as the quality of the studies that they include. If the studies are not very good, then the review will not be very good either. Large randomized controlled trials are expensive and take time. And sometimes it would not be ethical to do a study in which some patients 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 doing something to them. While these studies are cheaper and faster than randomized controlled trials, their results are not so 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. Researchers observed 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.⁴ To find out if beta carotene really did prevent cancer and heart disease, doctors needed to do a randomized controlled trial. The observational study wasn't good enough to answer the question: "Does beta carotene keep people from getting cancer and heart disease?" When the better quality study was done (people were randomly given either beta carotene or placebo pills) beta carotene did not work. In fact, it looked like beta carotene might increase the risk of getting cancer.⁵ Laboratory studies are another type of study. The results of these studies are often reported in the press. But they won't really play much of a part in helping you make decisions about treatments that are available now. For instance, in May 1998, thousands of desperate people with cancer phoned their doctors to ask about a front-page article in The New York Times.⁶ This article mentioned two drugs that had been shown to cure cancer. But the drugs had only been tested in mice. The article said this, but many readers overlooked this information because they were so excited to read about a cure. Just because a treatment has been shown to work in animals in laboratory experiments, doesn't mean it will work in humans. In fact, most drugs that have been shown to cure cancer in mice do not work in people. 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 makes it hard to do a study because everyone thinks they already know that a certain treatment works. This is often true for operations and orthopedic treatments. It can make it hard to know what is the best treatment. For example, if you break your wrist, you can either put it in a plaster cast or have surgery. If you have surgery, this usually involves inserting pins or other devices to hold your bones in place while they heal. But there is not enough evidence from studies to tell when surgery is a better choice.Many things doctors do are not supported by good-quality evidence. This is usually because the studies have not been done. A treatment may work even if there is no evidence that it does, but no one can say for sure that it does work. All the treatments described in Consumer Reports Health.org include links to the original reviews of research articles in Clinical Evidence.You can find original research studies in medical journals. They are written for doctors, and some of them may be difficult to understand. A medical dictionary can help. The main medical journals that your doctor looks at (and their Web site addresses) are :

• Annals of Internal Medicine (www.annals.org)
• BMJ (www.bmj.com)
• JAMA (http://jama.ama-assn.org)
• The Lancet (www.theLancet.com)
• The New England Journal of Medicine(www.nejm.org).

Government agencies like the Agency for Healthcare Research and Quality (www.ahcpr.gov) and the National Institutes of Health (www.nih.gov) have guidelines written for patients. These tell you what treatment you should be offered.Some of the reviews done by the Cochrane Collaboration (www.cochraneconsumer.com) are written for patients. And there is a section on how to make sense out of research.Healthfinder (www.healthfinder.gov) is a government site recommended by the Agency for Healthcare Research and Quality. You can use our information to help you make the decisions you face. If you are deciding to have surgery on your knee for osteoarthritis, for example, our information can help you discuss it with your doctor. You will need to consider your own values when you make decisions about your treatment. You may want to avoid surgery or at least try physical therapy. Or your pain may be keeping 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 evidence may not be able to tell you which treatment is best. The evidence 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. If you use our information, you will have read information based on the same research papers that your doctor has read.