Research Design in Clinical Psychology

Single-case experimental designs refer to arrangements that allow experimentation with the individual subject as well as with groups. The methodology is different from the usual group research and relies on ongoing assessment over time, assessment of baseline (pre-intervention functioning), and the use of multiple phases in which performance is evaluated and altered. Three major design strategies, ABAB, multiple-baseline, and changing-criterion designs, are highlighted. The designs vary in the way in which intervention effects are demonstrated and the requirements for experimental evaluation. However, the logic of the designs in demonstrating causal relations is the same in which ongoing assessment across different phases is used to describe, predict, and test predictions as changes are made in the conditions to which participants are exposed. Data evaluation of the results of single-case designs usually relies on nonstatistical methods referred to as visual inspection. Multiple criteria to invoke this method are detailed. Single-case designs have special strengths. These include the ability to: evaluate interventions in everyday settings without the need of control groups or random assignment, provide feedback on the effectiveness of an intervention while that intervention is underway, permit beginning the intervention on a small scale before any larger scale extension, permit evaluation of whether an intervention genuinely is effective with a given individual, and study rare conditions for which group studies are not feasible.