Supplementary Material for: Effects of Skip-Logic on the Validity of Dimensional Clinical Scores: A Simulation Study

Structured assessment of clinical phenotypes is a burdensome procedure, largely due to the time required. One method to alleviate this is “skip-logic,” which allows for portions of an interview to be skipped if initial (“screen”) items are not endorsed. The bias that skip-logic introduces to resultant continuous scores is unknown and can be explored using Item Response Theory. Interview response data were simulated while varying 5 characteristics of the measures: number of screen items, difficulty (clinical severity) of the screens, difficulty of non-screen items, shape of the trait distribution, and range of discrimination parameters. The number of simulations and examinees were held constant at 2,000 and 10,000, respectively. A criterion variable correlating 0.80 with the measured trait was also simulated, and the outcome of interest was the difference between the correlations of the criterion variable and the two estimated scores (with and without skip-logic). Effects of the simulation conditions on this outcome were explored using ANOVA. All main effects and interactions were significant. The largest 2-way interaction was between number of screen items and average item discrimination, such that the number of screen items had a large effect on bias only when discrimination parameters were low. This, among other interactions explored here, suggests that skip-logic can bias results using continuous scores; however, the effects of this bias are usually inconsequential. Skip-logic in clinical assessments can introduce bias in continuous sum scores, but this bias can usually be ignored.