**Kevin Tarlow, PhD**

Counseling Psychologist

**ITSSIM: Interrupted Time-Series Simulation**

- ITSSIM is a computer simulation method for analyzing single-case experimental data. ITSSIM models level, trend, variability, and autocorrelation parameters, and it yields effect size estimates appropriate for evidence-based clinical practice and meta-analysis.
- ITSSIM is accessible via free software download and requires no previous statistical computing experience.
- View a screenshot of ITSSIM software used to analyze an AB single-case data set.

**How Does ITSSIM Work?**

ITSSIM uses Monte Carlo simulation to estimate an effect size for an AB single-case data set. Essential to ITSSIM is the assumption that one observed single-case data set can be explained by many plausible intervention effects. Therefore, unlike other single-case statistical methods, ITSSIM effect sizes are not calculated from observed data; instead, ITSSIM effect sizes are calculated from many simulated time-series that are based on a range of conditions which could plausibly account for the observed data. An ITSSIM analysis proceeds in three stages:

**Parameter Estimation.**Level, trend, variability, and autocorrelation parameters (and their standard errors) are estimated from the observed data.**Time-Series Simulation.**100,000 artificial time-series are simulated based on the A phase parameter estimates, and another 100,000 artificial time-series are simulated based on the B phase parameter estimates. These time-series represent different null effects and intervention effects that could plausibly explain the observed A phase data and B phase data, respectively.**Effect Size Calculation.**Effect size statistics (including*d*and*r*) are estimated from the two distributions of simulated time-series means.

**Download**

- ITSSIM for Windows (18 KB)
- ITSSIM for Mac (9 KB)

**How to Cite:** Tarlow, K. R. (2018). *ITSSIM: Interrupted Time-Series Simulation, Version 1.0.* College Station, TX: Author. Retrieved from http://www.ktarlow.com/stats

**See Also:** Tarlow, K. R., & Brossart, D. F. (in press). A comprehensive method of single-case data analysis: Interrupted Time-Series Simulation (ITSSIM). *School Psychology Quarterly.* (preprint)

© 2016–2018 Kevin Tarlow