Interrupted time series design: a useful approach for studying interventions targeting participation.

Comparative effectiveness research (CER) strives for evidence to inform clinical decisions for specific clients in typical health care settings. While the randomized controlled trial (RCT) is well-aligned with the objectives of CER, this design may not be feasible or applicable to all research questions, particularly those pertaining to clinical decision making and individually based change. It is important, therefore, to consider alternative approaches, especially when studying complex and subjective outcomes such as children's participation. We propose the use of interrupted time series (ITS) quasi-experimental design for its potential application in determining the effectiveness of participation-focused interventions. In this perspective, ITS design is described, ascertaining its advantages and limitations, and suggestions are provided to overcome challenges to implementation. Results of a case study using the ITS approach to evaluate changes in participation of an adolescent with physical disabilities are described. Finally, strategies to implement this design in practice are suggested.