What does a major condition change line represent on a graph?

A major condition change line on a graph is represented by a solid vertical line. This line indicates a significant change in the conditions under which data were collected, such as the introduction of a new intervention or a change in the setting. By using a solid vertical line, it clearly demarcates the different phases of the data collection, allowing for easy visualization and interpretation of the effects of different conditions on behavior being studied. The solid line helps observers quickly identify where one phase ends and another begins, which is crucial for analyzing trends and making data-driven decisions in behavior analysis.