Guides to Use of Medical Literature
In analyzing the results of a published medical study, you must have confidence that the results of the study are valid - i.e. that they conclusions follow directly from the observations - and that you understand the results of a treatment. A short synopsis of two articles on medical studies published in the Journal of the American Medical Society (JAMA) is given below. The two articles are:
Are the results of the study valid?: Do the results represent an unbiased estimate of a treatment's positive effects or of a potential toxic effect of exposure or have they been influenced in some systematic fashion to lead to a false conclusion? Several factors must be considered?
A. Where there clearly identified comparison groups (experimental vs. control) that were similar with respect to important determinants of Outcomes other than the one of interest - i.e. the dependent variable? Three kinds of trials have been used in such assessments:
B. Were the exposures to potentially toxic agent and the outcomes (of RCT and cohort studies) measured the same in both experimental and control groups? For example, in a case control study, when asked about prior exposure to solvents, patients in the experimental group (with leukemia) might be more likely to recall and report previous exposure because of greater motivation (recall bias) or greater probing by an interviewer (interviewer bias). Exposures to potentially toxic agents should also be for a similar length. In a cohort study, a three-fold increase risk of cancer in radiation workers might be explained by a physician who was aware of the risk doing a more thorough assessment of the patient which might detect disease earlier or disease that would ordinarily go undetected (surveillance bias).
C. Were the patients available for follow-up for a sufficiently long enough period of time? If patients are not available for follow-up, the validity of the study might be compromised since that that remain available might have different prognosis than those who aren't available.
D. Were patients analyzed in the groups to which they were randomized? If someone in a experimental group taking a drug become noncompliant and don't take the medication, they should not be excluded from the analyses. Often these patients fared worse. Excluding them (while leaving similar patients in the control group) leaves behind those who might have gotten better, and removes the unbiased nature of the RCT.
E. Were patients, clinicians, and study personnel "blind" to treatment? If a patient knows they are on a new therapy, they will have an opinion about its efficacy, as will the practitioner and others involved in the study. The opinions can systematically distort aspects of the treatment, reporting of outcomes, and introduce bias of the medical personal into the assessment of the treatment efficacy. Best way to avoid is performing a double-blind study (for drug studies, using a placebo for the control group and target drug for the experimental group).
You should be able to differentiate among these methods, and understand the nature of blind and control studies, as well as the various biases.