174 Chapter 8 We will now explore two methodologies that could enhance physiotherapy research broadly and specifically improve our understanding of adherence in patients LBP. The first is the interrupted time series design (ITS) (34). The ITS design is a quasi-experimental approach used to measure outcomes at various points before, during, and after an intervention within a patient group. This approach enables a detailed comparison of changes in outcomes over time, allowing researchers to assess the effectiveness of an intervention by examining shifts in trends and levels of the outcomes of interest before and after its implementation. The ITS design is particularly well-suited for examining how healthcare interventions are implemented within specific settings. Furthermore, due to the collection of multiple different outcomes at multiple points prior to, during, and after implementation of a new intervention, this design also allows researchers to study temporal changes in (clinical) outcome and the associations between outcomes and their changes. For example, the ITS design would allow study of the relationship between changes in pain or disability over time and adherence trajectories over time. An advantage of the ITS design for use in physiotherapy research is its ability to utilize outcome measures from routine care in the analysis, significantly reducing the administrative and resource burdens associated with conducting such studies. The ITS design also has its limitations. For instance, the ITS design requires multiple measurements within each period to ensure reliability, typically three or more, leading to increased data collection efforts. Additionally, determining the adequate sample size remains a challenge, introducing uncertainty in the study’s statistical power and conclusions. Analyzing data from an ITS study necessitates specialized statistical techniques, expertise, and software, which might not be readily accessible to all researchers. This requirement can pose significant challenges in effectively conducting and interpreting ITS analyses (34). Lastly, the analyses of data collected using the ITS design involves comparing group level trends and changes in outcomes, reducing its viability when individual change is of interest. The second research design that might be more appropriate for physiotherapy research are the single case experimental designs (SCEDs), which are “the prospective, intensive, and experimental study of an individual who serves as his or her own control” (35). SCEDs, being experimental, generate quantitative data, distinguishing them significantly from case reports, which are qualitative in nature. This distinction highlights the strength of SCEDs in yielding specific, data-driven insights into how individual patients respond to various treatments, enabling a deeper understanding of the efficacy of therapeutic interventions. Furthermore, SCEDs enable the examination of how individual variability changes over time on different outcomes or factors, as well as the exploration of the relationships between these variations. Several types of SCEDs exist, such as the withdrawal/reversal design, changing criterion design, or multiple-baseline design), and are designed to determine a causal relationship between an intervention and clinical outcomes (36). The
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