Abstract

BackgroundRandomised controlled trials (RCTs) are considered the gold standard when evaluating the causal effects of healthcare interventions. When RCTs cannot be used (e.g. ethically difficult), the interrupted time series (ITS) design is a possible alternative. ITS is one of the strongest quasi-experimental designs. The aim of this methodological study was to describe how ITS designs were being used, the design characteristics, and reporting in the healthcare setting.MethodsWe searched MEDLINE for reports of ITS designs published in 2015 which had a minimum of two data points collected pre-intervention and one post-intervention. There was no restriction on participants, language of study, or type of outcome. Data were summarised using appropriate summary statistics.ResultsOne hundred and sixteen studies were included in the study. Interventions evaluated were mainly programs 41 (35%) and policies 32 (28%). Data were usually collected at monthly intervals, 74 (64%). Of the 115 studies that reported an analysis, the most common method was segmented regression (78%), 55% considered autocorrelation, and only seven reported a sample size calculation. Estimation of intervention effects were reported as change in slope (84%) and change in level (70%) and 21% reported long-term change in levels.ConclusionsThis methodological study identified problems in the reporting of design features and results of ITS studies, and highlights the need for future work in the development of formal reporting guidelines and methodological work.

Highlights

  • Randomised controlled trials (RCTs) are considered the gold standard when evaluating the causal effects of healthcare interventions

  • After removing duplicates (187) and excluding 2552 titles and abstracts that did not meet the inclusion criteria, 372 full-text studies were assessed for eligibility

  • 256 articles were excluded with the majority (170) having too few time points

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Summary

Introduction

Randomised controlled trials (RCTs) are considered the gold standard when evaluating the causal effects of healthcare interventions. When RCTs cannot be used (e.g. ethically difficult), the interrupted time series (ITS) design is a possible alternative. ITS is one of the strongest quasi-experimental designs. The aim of this methodological study was to describe how ITS designs were being used, the design characteristics, and reporting in the healthcare setting. The gold standard for evaluating the causal effect of an intervention is a randomised controlled trial (RCT). Researchers must consider alternative designs to evaluate interventions and quasi-experimental studies are one possible solution [4]. Quasi-experimental studies do not use randomisation and may use both preand post-intervention data.

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