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Use of interrupted time series analysis in health services research

Although randomized control trials (RCTs) are the ‘gold standard’ to evaluate treatment effects in health care, they are frequently not practical, ethical or politically acceptable in the evaluation of many health system or public health interventions. In the absence of an RCT, evaluations often use quasi-experimental designs such as a pre-post study design with measurements before and after the intervention period, such as interupted time series (ITS). An ITS compares the intercept and slope of the regression line before the intervention with the intercept and slope after intervention. A one-time baseline effect of the intervention without influencing the secular trend can be detected as an intercept change. If the intervention changed the secular trend, there will also be a significant difference in the slope between the two periods. Use of ITS in biomedical research is described in more detail in an article published by Utz Pape and colleagues in the Journal of the Royal Society of Medicine.

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