OSU logo Oklahoma State University
Center for Health Sciences
Medical Physiology - Evidence-Based Medicine
Printer Friendly


What is EBM?

Patient Care Model
Life-long Learning
Why is EBM Important?
Available Evidence?
EBM Issues

The Well-built Question

The EBM Process
Anatomy of a Question

Finding Evidence

Selecting a Resource
Searching the Resource
Reviewing Search Results
Returning to the Patient

Evaluating Evidence

Evaluating the Validity
Validity Questions


Knowledge Test

Multiple Sclerosis
Case #2
Case #3
Case #4




Evaluating the Validity of a Therapy Study

The article selected to demonstrate the procedure for evaluating the validity of a therapy study is:

The effect of digoxin on mortality and morbidity in patients with heart failure.
The Digitalis Investigation Group. New England Journal of Medicine February 20, 1997; 336(8):525-533.
The Massachusetts Medical Society has given us permission to make this article available for this tutorial.

The next step is to read the article and evaluate the study.

There are three basic questions that need to be answered for every type of study:

  • Are the results of the study valid?

  • What are the results?

  • Will the results help in caring for my patient?

This tutorial will focus on the first question: are the results of the study valid? The issue of validity speaks to the "truthfulness" of the information. The validity criteria should be applied before an extensive analysis of the study data. If the study is not valid, the data may not be useful.

The evidence that supports the validity or truthfulness of the information is found primarily in the study methodology. Here is where the investigators address the issue of bias, both conscious and unconscious. Study methodologies such as randomization, blinding and accounting for all patients help insure that the study results are not overly influenced by the investigators or the patients.

Evaluating the medical literature is a complex undertaking. It is not the intention of this tutorial to downplay that intellectual process or to make you an expert on evaluating the evidence. This session will provide you with some basic criteria and information to consider when trying to decide if the study methodology is sound. You will find that the answers to the questions of validity may not always be clearly stated in the article and that clinicians will have to make their own judgments about the importance of each question.

Once you have determined that the study methodology is valid, you must examine the results and their applicability to the patient. Clinicians may have additional concerns such as whether the study represented patients similar to his/her patients, whether the study covered the aspect of the problem that is most important to the patient, or whether the study suggested a clear and useful plan of action.

Note: The questions that we used to test the validity of the evidence are adapted from work done at McMaster University. See the References/Glossary unit: 'Users' Guides to the Medical Literature.'

We now go to Validity Questions