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Summated scales are often used in survey instruments to probe underlying constructs that the researcher wants to measure. These may consist of indexed responses to dichotomous or multi-point questionnaires, which are later summed to arrive at a resultant score associated with a particular respondent. Usually, development of such scales is not the end of the research itself, but rather a means to gather predictor variables for use in objective models. However, the question of reliability rises as the function of scales is stretched to encompass the realm of prediction. One of the most popular reliability statistics in use today is Cronbach's alpha (Cronbach, 1951). Cronbach's alpha determines the internal consistency or average correlation of items in a survey instrument to gauge its reliability. This paper will illustrate the use of the ALPHA option of the PROC CORR procedure from SAS(R) to assess and improve upon the reliability of variables derived from summated scales.
J.M. Vieira dos Santos (Fri,) studied this question.