The Cost of Increased Validity: Combining a Multiple Baseline Design with an ABAB Design

Abstract

A previous feasibility study, degradation of pilot flight performance when transitioning from digital instrumentation to analog instrumentation for the first time, was replicated using two single case research designs (SCDs). The validity of SCDs has often been questioned by researchers who use between-group designs. However, within the research fields using single case research, it is suggested that the validity of SCDs can be improved by systematic replication of single case experiments. This study investigated whether validity could be improved by systematic replication of single case experiments by comparing two SCDs: the multiple baseline design (MBD), which increases replications across subjects to improve validity, and the combined design, which increases replications both across and within subjects and may provide greater improvement in validity. The two designs were compared in terms of results, validity, and cost. The results of the data analyses did not provide any significant advantages or disadvantages for either design, and the improvement in validity of the combined design came at a considerable increase in cost.