Final answer:
The baseline stage sets a reference point for behavior or performance before intervention in a stable baseline design, allowing post-intervention comparison and control for other variables.
Step-by-step explanation:
The baseline stage in a stable-baseline design is crucial for understanding the current behavior level or performance before any treatment or intervention is applied. This stage serves as a control or reference point, allowing researchers to measure the effects of the intervention during subsequent stages of the design by comparing post-intervention data to the baseline data. During the baseline period, researchers meticulously record the behavior or performance, establishing a pattern against which any changes can be detected. The baseline is important not only for assessing the efficacy of the intervention but also for ruling out other variables that could account for changes in behavior.