Abstract
Analytic epidemiological studies cover a large spectrum of study methodologies, ranging from noninterventional observational studies (population-based, case-control, or cohort studies) to interventional studies (clinical trials). Herein, we review the different research methodologies or study designs and discuss their advantages and disadvantages in the context of chronic obstructive pulmonary disease (COPD) pharmacotherapy. Although randomized controlled trials (RCTs) are considered the "gold standard" for evaluating the efficacy and safety of an intervention, observational studies conducted in a real-world scenario are useful in providing evidence on the effectiveness of the intervention in clinical practice; understanding both efficacy and effectiveness is important from the clinician's perspective. Pragmatic clinical trials that use real-world data while retaining randomization bridge the gap between explanatory RCTs and noninterventional observational studies. Overall, different study designs have their associated advantages and disadvantages; together, findings from all types of studies bring about progress in clinical research as elucidated through examples from COPD research in this paper.