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SUNY Downstate Medical Research Library of Brooklyn: Evidence-Based Medicine Course

Background Information

Background information is sought when a learner has general clinical questions regarding a topic such as what is the disorder; what causes it; how does it present; what are some treatment options.  These questions can be answered by using "background" resources such as textbooks (both in print and electronic) and narrative reviews in journals which give a general overview of the topic. 

Cohort Study

A cohort study is a study in which researchers compare two groups over a period of time. At the start of the study, one of the groups has a particular condition or receives a particular treatment, and the other does not. At the end of a certain amount of time, researchers compare the two groups to see how they did. 

Control Group

The control group of a study is a group that receives a treatment other than the one being studied (for instance, a placebo pill that looks identical to the medication being studied but that has no active ingredients). Control groups are necessary since we need to be able to compare the results of the treatment being studied to available alternatives. For instance, the fact that 90% of all patients taking treatment A for condition B recovered within one year tells us nothing unless we know the percentage of patients who recover from condition B within one year with no treatment at all!   Where placebos cannot be used, the control group is defined as to "standard" therapy or to the use of another intervention.


Diagnosis problems are questions about the degree to which a particular test is reliable and clinically useful, generally asked in order to decide whether a patient of yours would get enough benefit (a decision about diagnosis and therapy to influence clinical decisions) from the test, on average, to justify having it done. Most articles on diagnosis compare the results of the diagnostic test being studied to the results of another standard test that is regarded as being definitive - a 'gold standard' test. 

Double Blind

A double blind study is one in which neither the patients nor the health care personnel involved in treatment know whether a particular patient is receiving the treatment being studied or is part of the control group. 

Evidence-Based Medicine

The use of simple rules of logic and science to find, appraise and apply evidence from research to the care of individual patients. 

Foreground Information

Foreground information answers specific questions a clinician has regarding a patient.  Foreground resources can be divided into primary sources such as original research articles published in journals; and secondary sources such as  systematic reviews of the topic, and synopses and reviews of individual studies. 


Harm problems are questions about the relationship between a disease or therapy and a possible cause. For example, does a diet rich in saturated fats increase the risk of heart disease, and if so, by how much? 

Placebo Effect

This effect is one in which patients who believe that they are receiving an effective treatment for their condition tend to show substantial improvement, even if they are actually only receiving a dummy treatment such as a sugar pill. This effect is surprisingly strong, and is the main reason for the use of the 'double blind' experimental design. The effect is inconvenient for research, but of course therapeutically it is very useful and you try your best to always have it on your side!  In 2001, a debate about the value and ethics of placebo controls emerged which will have to be followed.

Predictive Value of Tests

In screening and diagnostic tests, the probability that a person with a positive test is a true positive (i.e., has the disease), is referred to as the predictive value of a positive test; whereas, the predictive value of a negative test is the probability that the person with a negative test does not have the disease. Predictive value is related to the sensitivity and specificity of the test.

Primary Source

A primary source is firsthand testimony or direct evidence concerning a topic under investigation. 


Prognosis problems are questions about a patient's future health, life span, and quality of life in the event that s/he chooses a particular treatment option. For instance, how do the lifespan and quality of life of an elderly patient undergoing surgery for prostate cancer compare with those for a similar patient who chooses not to undergo the surgery? 

Secondary Source

Secondary sources are summaries and analyses of the evidence derived from and based on primary sources. A secondary source is a work that appraises, interprets or analyzes.   It is generally at least one step removed from the evidence.


Therapy problems are questions about what treatment, if any, to give a patient, and what the outcomes of different treatment options might be.