Observational studies and evidence-based practice: Can't live with them, can't live without them

Stroup et al1 define an observational study as “an etiologic or effectiveness study using data from an existing database, a cross-sectional study, a case series, a case-control design, a design with historical controls, or a cohort design.” Generally, there are several major problems with the use of observational studies in systematic reviews of evidence for a treatment procedure. The first is that since all observational studies lack randomization, true assessment of efficacy is not possible. Furthermore, it is not possible to determine what biases may have influenced the results, both from the provider and the patient. Analytically, results from observational studies either cannot be pooled for a meta-analyses or can be done so only with caution.