A GUIDE TO INTERPRETING EPIDEMIOLOGIC STUDIES ON THE ETIOLOGY OF BACKPAIN

Understanding disease etiology is key for effective preventive or ther apeutic interventions. Knowledge about risk factors is useful to the c linician to answer patients' questions about the possible cause(s) of their presenting disorders. This article describes the three most comm on types of etiologic studies using examples from the published litera ture on the risk factors for back pain. Cohort studies typically follo w a group of ''healthy'' people forward in time to assess disease outc ome after risk factors have already been measured. Case-control studie s use people selected on the basis of outcome status; risk factors are assessed after the fact. Although more prone to bias than cohort stud ies, case control studies are more common in back pain research becaus e of the ease of examining several risk factors simultaneously and the expense of cohort studies. Prevalence studies use a random sample of people collected at a single point in time; consequently there is no p redetermined number of ''cases'' and ''controls,'' their numbers depen ding on the prevalence of disease and exposures in the samples. To ass ist in the interpretation of research findings this paper presents a g eneral framework for assessing the strengths and weaknesses of an indi vidual study. Case-control studies are discussed in more detail becaus e they are so commonly encountered in the etiologic literature. Finall y, because the evidence from a single study, no matter how well design ed and executed, is never enough on its own to decide if a risk factor is causal or not, the paper concludes by briefly summarizing the crit eria for inferring causation using the full body of available biologic and epidemiologic literature.