Using forecast modelling to evaluate treatment effects in single-group interrupted time series analysis

Journal of Evaluation in Clinical Practice
Ariel Linden

Abstract

Interrupted time series analysis (ITSA) is an evaluation methodology in which a single treatment unit's outcome is studied serially over time and the intervention is expected to "interrupt" the level and/or trend of that outcome. ITSA is commonly evaluated using methods which may produce biased results if model assumptions are violated. In this paper, treatment effects are alternatively assessed by using forecasting methods to closely fit the preintervention observations and then forecast the post-intervention trend. A treatment effect may be inferred if the actual post-intervention observations diverge from the forecasts by some specified amount. The forecasting approach is demonstrated using the effect of California's Proposition 99 for reducing cigarette sales. Three forecast models are fit to the preintervention series-linear regression (REG), Holt-Winters (HW) non-seasonal smoothing, and autoregressive moving average (ARIMA)-and forecasts are generated into the post-intervention period. The actual observations are then compared with the forecasts to assess intervention effects. The preintervention data were fit best by HW, followed closely by ARIMA. REG fit the data poorly. The actual post-intervention observations were ab...Continue Reading

References

Jan 23, 2004·Disease Management : DM·Ariel LindenNancy Roberts
Oct 1, 2013·BMC Medical Research Methodology·Ariel Linden
Mar 24, 2016·Journal of Evaluation in Clinical Practice·Ariel Linden, Paul R Yarnold
Apr 20, 2016·Journal of Evaluation in Clinical Practice·Ariel Linden, Paul R Yarnold
Sep 16, 2016·Journal of Evaluation in Clinical Practice·Ariel Linden
Dec 22, 2017·Journal of Evaluation in Clinical Practice·Ariel Linden
Feb 21, 2018·Journal of Evaluation in Clinical Practice·Ariel Linden
Apr 17, 2018·Journal of Evaluation in Clinical Practice·Ariel Linden

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Citations

Jul 14, 2020·Research Synthesis Methods·Simon L TurnerJoanne E McKenzie

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