How do the interrupted and the equivalent time-series designs differ?

Question

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The Answer is Interrupted time-series design and equivalent time-series design are both quasi-experimental research designs used to evaluate the effects of interventions over time. However, they differ in their structure and the way they control for potential confounding variables.

Interrupted Time-Series Design:
An interrupted time-series design involves collecting data at multiple time points before and after an intervention is implemented. The key feature of this design is the "interruption" of the time series by the introduction of the intervention. Researchers look for changes in the trend or level of the outcome variable that can be attributed to the intervention. This design is particularly useful when randomization is not possible, and it can provide strong evidence for causality if the pattern of change is consistent with the hypothesized effect of the intervention.

The strength of the interrupted time-series design lies in its ability to detect changes in trends over time. However, it can be vulnerable to confounding factors that also change around the time of the intervention, such as other policy changes or seasonal effects.

Equivalent Time-Series Design:
An equivalent time-series design, also known as a non-equivalent control group time-series design, adds a comparison group to the interrupted time-series design. This comparison group is not exposed to the intervention. By including a control group, researchers can compare the trends and changes in the outcome variable for both the intervention group and the control group. This helps to control for external factors that might be influencing the outcome variable, as any such factors should affect both groups similarly.

The equivalent time-series design is stronger than the simple interrupted time-series design because it helps to account for alternative explanations for the observed changes, other than the intervention. This design is particularly useful when researchers suspect that other factors might be influencing the outcome variable and when these factors cannot be easily measured or controlled for.

In summary, while both designs are used to assess the impact of interventions over time, the equivalent time-series design provides a more robust approach by including a control group to help account for potential confounding variables. The interrupted time-series design, on the other hand, does not include a control group and focuses solely on the changes in the outcome variable following the intervention.

How Do the Interrupted and the Equivalent Time-Series Designs Differ