Sources of Information
Most doctors rely heavily on their experience: what they have learned from diagnosing and treating people with similar problems. However, doctors also read medical books and journals, consult with colleagues, and refer to other resources such as health sites on the Internet for more information on specific problems and to keep up with new information generated by medical research. They may also review recommendations (practice guidelines) published by groups of experts.
People who need health information rely most heavily on their doctors. But many people also turn to an ever-growing number of resources in print and on the Internet.
As new research findings are published, a doctor evaluates studies and considers how their findings might be applied. Different types of studies provide different types of information.
A cross-sectional study compares groups of people at the same point in time. Such a study compares test results of people who do and do not have a given disease and is often used to evaluate how well tests help diagnose diseases. A case-control study compares the histories of people who are similar except for the condition that is being studied. Such a study is often used to understand the cause or causes of a disease. In a cohort study, people are studied for a similar period of time, which varies from hours to decades, depending on what is being studied. A cohort study might be used to determine the effect of a disease on people over time (prognosis).
A clinical trial is considered the most rigorous type of study. In a controlled clinical trial, one group of people gets a particular treatment or test while the other groups (control groups) get different treatments or tests or no treatment or test at all. People may be assigned to the groups at random in a randomized controlled clinical trial. Conditions in a clinical trial are restricted, so only people with similar characteristics participate.
Sometimes studies are done to compare the relative costs of different approaches to diagnosis and treatment. These are called cost-effectiveness and cost-benefit studies. They may help a doctor consider the effects of decisions from society's perspective, but they may be less helpful when the doctor is considering decisions for a particular person.
Because of differences in the way studies are planned and carried out, even studies that are intended to evaluate the same thing may produce conflicting results. One method to try to resolve these conflicts is to prepare a summary of the findings of all studies that pertain to the topic and rigorously compare and evaluate them. This type of study is called a systematic review. Another method that tries to resolve conflicting results of studies is called meta-analysis; a meta-analysis combines the studies' results mathematically and then compares them.
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