ABSTRACT
Among behavior analysts, single-case designs have become a popular alternative to more traditional group experiments. Although single-case designs have numerous strengths both philosophically and practically, they also have potential weaknesses in the areas of analysis and infer ence. In attempts to address a major analytic issue (i.e., the limited numbers of observations), the use of frequent and repeated measures is often suggested (Barlow & Hersen, 1984). The collection of data at sev eral points in time, however, creates the potential for "testing" and "instrumentation" (Campbell & Stanley, 1966) as threats to internal va lidity (Horn & Heerboth, 1982). The primary focus of this chapter is that undetected cyclical trends in behavior (or factors correlated with the target behavior) may confound estimates of treatment effects. Moreover, cyclicity, even when detected, complicates the interpretation of data and remains one of the most neglected issues in single-case research (Barlow & Hersen, 1984).
