What is depicted by a phase change line on a line graph?

The phase change line on a line graph is specifically used to indicate a significant transition from one phase of the study to another, typically marking the shift from a baseline phase to an intervention phase. This line serves as a visual cue for viewers to quickly identify where a change in treatment or condition occurs, allowing them to assess the effects of the intervention on the data collected.

By marking this transition clearly, it aids in the analysis of how the behavior or performance metric of interest responds to the intervention that follows the baseline period. This aspect is crucial in research and applied behavior analysis, as it helps in determining whether the intervention has had a notable impact on the subject's behavior compared to the baseline measurements taken prior to the intervention.