Level, Trend and Variability in Graphs

Visual Analysis and the Line Graph

In applied behavior analysis, line graphs commonly display behavior measurements collected across sessions or time periods, including measurements collected with continuous or discontinuous methods. Behavior analysts rely on visual analysis as their primary method to interpret the data shown on these graphs. When you enter session data accurately and promptly, you help your supervisor perform reliable visual analysis. The horizontal axis, or x-axis, typically displays time, calendar dates, or consecutive treatment sessions. The vertical axis, or y-axis, displays the quantitative measure of the target behavior, such as frequency, rate, or percentage.

Graphs also feature condition change lines to mark documented shifts in conditions, such as moving from baseline to an intervention. A solid vertical line typically represents a major phase change, like introducing a completely new teaching strategy. A dashed vertical line typically marks a minor modification within an ongoing condition, such as adjusting a prompt delay. Data points across any condition change line are generally not connected by a data path. If an unexpected event occurs during a session, such as an unplanned fire drill, it is typically noted separately rather than marked with a condition change line.

Visual analysis begins by evaluating the data within a single condition before comparing data across different conditions. When looking at data within an individual phase, the observer examines the number of data points along with three fundamental properties: level, trend, and variability. Understanding these properties helps you describe client progress clearly and talk about performance with your supervisor using precise behavioral terms.