How and why study designs affect the nature and validity of study results: appearance versus true knowledge. Part II

Patients often do not respond optimally to the first medication tried. Hence, switching among classes of medications-and even within a class-for a given indication is common in clinical practice. Such switches are often based on clinical judgment or experience, but it is preferable to base such decisions on valid empirical data when available. The first part of this two-part series described findings from early sequential treatment trials of selective serotonin reuptake inhibitors (SSRIs) to illustrate how data derived from suboptimally designed trials pro-duce only the appearance of knowledge rather than reliable knowledge. Although these early trials suggested that 50% to 60% of patients who had not benefited from one SSRI could benefit when switched to a second SSRI, this conclusion is not supported by pharmacologic data or recent research findings. Part I of this series reviewed differences between treatment in clinical trials and routine practice settings that might account for those discrepancies. This second part of the series describes five different types of study designs, ranging from the least to the most rigorous, to help clinicians decide how much credence to give to results produced by these different types of studies and thus how to better recognize when studies are providing the appearance rather than the substance of knowledge. (Journal of Psychiatric Practice 2009;15:402-407).