Refining the measurement of psychological adjustment in cancer

We describe five phases of research desired to refine the psychometric properties of the PAC, a measure of psychological adjustment in cancer patients. PAC items were originally generated by modification of an existing diabetes instrument, and item discrimination examined differences between 91 cancer patients and 173 age-matched patients with diabetes. Cancer was considerably more stressful than diabetes but patients reported a similar range of qualitative responses. Focus group techniques were used to further refine the item set. A series of analyses in different samples identified six relatively stable factors and a Cronbach's alpha of 0.74-0.86. The test-retest correlation for the total PAC score was 0.92 and convergent validity was shown by a consistent pattern of association with criterion measures. In a randomised controlled trial, total PAC scores were shown to be sensitive to experimental manipulations of the medium, message, and context of cancer terminology. A factor replication study of the 53-item scale in a sample of 283 patients with melanoma resulted in a shorter 21-item, two-factor scale with superior psychometric properties.