Single-case designs (SCDs) are a class of research methods for evaluating intervention effects by taking repeated measurements of an outcome over time on a single case, both before and after the deliberate introduction of a treatment. SCDs are used heavily in fields such as special education, school psychology, social work, and applied behavior analysis. Several different operational procedures are commonly used to record direct observations of human behavior, ranging from continuous duration recording to interval recording methods. This methodological research will describe a model for behavioral observation data that allows definition of an intuitively interpretable, operationally comparable effect size, the prevalence odds ratio (POR). After defining the POR, the author describes basic estimators based on data from several different recording methods. The model described in this abstract provides a basis for defining an operationally comparable effect size, the prevalence odds ratio, that allows comparisons and meta-analytic summaries of treatment effects measured using different behavioral observation recording procedures. Tables and figures are appended.