Two types of interobserver reliability values may be needed in treatment studies in which observers constitute the primary data-acquisition system: trial reliability and the reliability of the composite unit or score which is subsequently analyzed, e.g., daily or weekly session totals. Two approaches to determining interobserver reliability are described: percentage agreement and "correlational" measures of reliability. The interpretation of these estimates, factors affecting their magnitude, and the advantages and limitations of each approach are presented.

This article describes and illustrates with two case studies a relatively novel form of the multiple-baseline design called the changing criterion design. It also presents the design's formal requirements, and suggests target behaviors and circumstances for which the design might be useful.

This paper uses a question-and-answer format to present the technical aspects of interrupted time-series analysis (ITSA). The reader should understand that he or she will not be able to perform an ITSA as a result of reading our paper. It is not intended as a cookbook for performing an ITSA. It is instead a description of the novel aspects of ITSA written in reasonably ordinary language. We have written the material that follows in a questionand-answer format. This format allows the reader the options of obtaining an answer to a specific question by turning to the relevant portion of the paper or obtaining a general understanding of ITSA and related issues by reading the paper straight through.