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Data from four studies were used to assess the psychometric properties of the 26 IQCODE items. The items were assessed in terms of item-total correlations, test-retest reliabilities, correlations with indicators of current cognitive functioning and correlations with indicators of premorbid cognitive functioning. These data were used to develop a 16-item short form. The short form was cross-validated in a new sample using dementia/delirium diagnosis as the validity standard. It was found to perform as well as the long form.
Anthony F. Jorm (1994) studied this question.