Analyzing Therapeutic Change Using Modified Brinley Plots: History, Construction, and Interpretation

The paper reviews the history, construction, and interpretation of modified Brinley plots, a scatter plot used in therapy outcome research to compare each individual participant's scores on the same dependent variable at Time 1 (normally pretreatment baseline; x-axis), with scores at selected times during or after treatment (y-axis). Since 1965 eponymously named Brinley plots have occasionally been used in experimental psychology to display group mean data. Between 1979 and 1995 a number of clinical researchers modified Brinley plots to show individuals' data but these plots have received little subsequent use. When constructed with orthogonal axes having the same origin and scale values, little or no change over time is shown by individuals' data points lying on or closely about the diagonal (45⁰_o) while the magnitude and direction of any improvement (or deterioration), outliers, and the extent of replication across cases shows via dispersion of points away from 45⁰_o. Interpretation is aided by displaying reliable change boundaries, clinical cutoffs, means, variances, confidence intervals, and effect sizes directly on the graph. Modified Brinley plots are directly informative about individual change during therapy in the context of concurrent change in others in the same (or a different) condition, clearly show if outcomes are replicated and if they are clinically significant, and make nomothetic group information, notably effect sizes, directly available. They usefully complement other forms of analysis in therapy outcome research.