The I2 Test for Selection Bias Risk Assessment in Single Trials: Recommended Simulated Comparator Trial (SCT) Settings.

Selection bias in clinical trials is a form of systematic error and may be detected using the I² test with a 0/>0% threshold (bias: I² > 0%, no bias: I² = 0%). The test operates on the premise that effective randomisation eliminates in-between study heterogeneity beyond the play of chance in a baseline variable meta-analysis of all the trial's baseline variables. Since the I² statistic was originally designed to measure in-between study heterogeneity in meta-analyses, the test requires the generation of at least two simulated comparator trials (SCTs). During this process, three parameters are set: SCT sample size (N), the minimum-maximum range of random values (R), and the number of generated SCTs to be used (SCT). Each of these parameters influences the 0/>0% threshold of the resulting I² point estimate, thereby affecting the test's sensitivity in indicating a positive result. The purpose of this technical report is to highlight the effect that SCT parameters have on the test's accuracy and to recommend appropriate parameter settings.