Assessing psychological distress in cancer patients: validation of a self-administered questionnaire

Screening for psychological distress in cancer patients is important, considering the high prevalence of psychiatric disorders responsive to treatment. The aim of this study is to test the psychometric properties of the Psychological Distress Inventory (PDI), a 13-item self-administered questionnaire developed to measure psychological distress in cancer patients.

The PDI was tested in three samples of 434 cancer patients. In the first sample (n = 102) it was administered with the State Trait Anxiety Inventory (STAI) and with the Eysenck Personality Questionnaire (EPQ). Its validity as a screening method for psychiatric disorders was evaluated through a clinical interview in the second sample (n = 107). The third sample (n = 225) provided information on the ability of the PDI to discriminate among patients in different clinical phases of disease and allowed an estimate of the prevalence of psychiatric disorders in these groups of patients.

A 0.88 alpha coefficient was obtained in the whole study sample. The correlations with the STAI scales were > 0.70. A positive correlation with neuroticism (r = 0.59) and a negative correlation with extroversion (r = -0.34) was observed. In the second sample, 67 patients (62.6%) received a psychiatric diagnosis according to the ICD-X criteria. The mean PDI scores were significantly lower for the 40 patients with no psychiatric diagnosis (mean 24.5) as compared with the 49 patients with adjustment disorders (mean 36.4) and with the 12 patients with depressive disorders (mean 40.8). The area under curve, estimated through a Receiver-Operating Characteristics analysis, was 0.88. A cut-off of 29 was associated with a 75% sensitivity and a 85% specificity. In the third sample, the lowest PDI scores were in patients with no evidence of disease (mean 24.7, 95% CL 23.0-26.4) as compared to patients undergoing antineoplastic treatment (mean 30.9, 95% CL 28.9-32.9) and to patients under palliative therapy (mean 36.0, 95% CL 34.0-37.9). The estimated prevalence of patients with psychiatric disorders in these three groups were respectively 5.0, 56.6 and 98.8%.

Our results suggest that the PDI is a reliable and valid tool for measuring psychological distress in cancer patients and to detect psychiatric disorders through a screening procedure.