Baseline

A baseline is an assessment of performance that allows educators or therapists to (a) determine current level of functioning, (b) predict future performance in the absence of any change in conditions, and (c) ascertain the effects of subsequent interventions (i.e., independent variables). A baseline consists of data collected under a specific set of conditions that are used to describe and predict behavior for the purpose of making comparisons. If behavior can be accurately described and predicted under baseline conditions, performance observed under those conditions can be compared to performance when the conditions are changed, as during intervention implementation. In the absence of baseline data, the success or failure of an intervention would remain unknown.

Typically, baseline data consist of several assessments of performance collected across time, such as across a number of days or sessions. Several assessments are necessary to determine whether a reliable pattern exists in the data. The pattern may indicate (a) stability (e.g., predictable directions or trends indicated), (b) systematic changes in behavior across assessment occasions (e.g., regular increasing or decreasing trends, or level or step changes), or (c) considerable variability in performance from session to session (e.g., irregular or cyclic patterns). Systematic changes refers to improvement or worsening during the baseline assessment period, whereas variability refers to “bounce” or fluctuations in the data from day to day. When performance is variable, an individual may perform at a high level on some days and a low level on others. The more variable the data pattern, the more difficult it is to discern trends or directions in the data over time or sessions. Confidence in conclusions about the effects of an intervention is higher if baseline data are relatively stable; that is, where baseline performance patterns do not indicate improvement and are not highly variable.

If behavior improves across time during baseline, one might be able to predict that the individual would achieve (or not) adequate levels of performance even if the treatment were not provided. The questions then become, How long will it take for adequate levels to be achieved? and, Is this time period acceptable for the learner? Baselines might be considered adequate if the data indicate that behavior is becoming worse, rather than better, prior to treatment. However, when worsening is noted, the assessment process itself may be associated with producing undesirable performance (a phenomenon known as reactive measurement). This type of effect could make changes in behavior that occur following intervention appear more impressive than they otherwise would have.

Where the variability is excessive in baseline, determining whether an improving or worsening trend is present is difficult. Further, high variability may result in such a substantial amount of overlap between baseline and intervention data that drawing conclusions regarding the presence of intervention effects may become difficult or impossible.

Although the primary use of a baseline condition is to provide a basis for comparison, observations conducted during baseline may also assist in planning interventions, in establishing criteria for the application of consequences, and in checking the accuracy of [Page 1156]subjective judgments regarding the frequency, duration, or intensity of behaviors.

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