Purpose: To describe common errors in the analyses and data presentation of a clinical case series and to suggest simple solutions.
Design: Instructional examples.
Methods: Problems with commonly used data analysis and reporting techniques in clinical case series are described using both theoretical examples and those from the literature.
Results: An analysis reporting the proportion of a series of patients with variable follow-up does not adequately account for the differential follow-up among patients and is a potentially misleading way to present data. Instead, the proportion of patients at presentation (or study entry) and the rate during follow-up should be reported. Similarly, an analysis in which the final visual acuity of a series of patients with variable follow-up is reported does not adequately account for the effect of time and also may be misleading. Reporting of the rates of visual acuity events during follow-up (e.g., falling below a specified threshold, such as 20/50 or worse) is preferred. Alternatively, when there is nearly complete follow-up, reporting the distribution of visual acuity at specified time points (e.g., 1 year after study presentation) is appropriate. Small case series should not be overinterpreted because of the effects of chance, and appropriate statistical analyses should be employed.
Conclusions: Clinical case series often suffer from several potential reporting flaws. Correction of these flaws would permit the proper interpretation of the data and allow for the ability to combine data from several case series to assemble more meaningful and reliable conclusions.