The Journal of Psychology, 1986, 121(6), 635-636.
Internal Inconsistency in the Eysenck Psychoticism Scale
JOHN J. RAY
School of Sociology, University of New South Wales, Australia
Department of Psychology, C. W. Post College
FOR SOME TIME, researchers have commented that the Eysenck Psychoticism (P) Scale is not factorially homogeneous (e.g., Stanley & Watkins, 1972). This makes it likely that the scale's reliability as measured by coefficient alpha is also low, because alpha is based on internal consistency. Alpha can in fact be calculated as a mean interitem correlation weighted by the number of items. It is no surprise, therefore, that Ray and Bozek (1981) found an alpha of only .68 for the 25-item P scale on an Australian sample. This is markedly less than what was found by Eysenck and Eysenck (1976) with their English samples. Because it could be argued that Australia is culturally less distant from Britain than the United States (e.g., Australia is also a monarchy), it is possible that if the scale works less well in Australia then it should work even less well in the United States.
The same questionnaire as that used by Ray and Bozek (1981) -- one in which the P Scale items were mixed in with those of several other scales -- was administered to a sample of respondents from Nassau County in New York State. Addressees for the survey were selected at random from the phone book. Two follow-up questionnaires were sent to non-respondents. Out of 500 initial addresses, a final total of 97 usable responses were received. Although the nonresponse effect ensured that the final sample was not random, the sample was probably more representative than the more usual sample of college students. The coefficient alpha observed for the scale was .48.
The Eysenck P Scale was designed for use with normals as well as with psychotics. Among normals it measures the politically relevant variable of tough-mindedness. The test of the P Scale on a general population sample was therefore a fair one. It failed the test strikingly: Shaw and Wright (1967) specified a reliability of .75 as the minimum acceptable in a research instrument. Because Nunnally (1967) argued that alpha is the best possible measure of reliability (better even than test-retest reliability) the finding of .48 did not even approach acceptable reliability. The problem becomes even more evident when we note that the mean interitem correlation for the P Scale was .04. The items, then, have very little in common. As far as U.S. respondents .are concerned, Eysenck's attempt to find a common personality factor underlying psychoticism is a failed experiment.
Eysenck, H. J., & Eysenck, S. B. G. (1976). Psychoticism as a dimension of per
sonality. London: Hodder.
Nunnally, J. C. (1967). Psychometric theory. New York: McGraw Hill.
Ray, J.J. & Bozek, R.S. (1981) Authoritarianism and Eysenck's 'P' scale. Journal of Social Psychology, 113, 231-234.
Shaw, M. E., & Wright, J. M. (1967). Scales for the measurement of attitudes. New York: McGraw Hill.
Stanley, G., & Watkins, D. (1972). A factorial study of Eysenck & Eysenck's Psychoticism, extraversion and neuroticism scales. Australian Psychologist, 7, 26-32.
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