Psychometric evaluation of 3-set 4P questionnaire.

This is a further development of a specific questionnaire, the 3-set 4P, to be used for measuring former ICU patients' physical and psychosocial problems after intensive care and the need for follow-up. The aim was to psychometrically test and evaluate the 3-set 4P questionnaire in a larger population. The questionnaire consists of three sets: "physical", "psychosocial" and "follow-up". The questionnaires were sent by mail to all patients with more than 24-hour length of stay on four ICUs in Sweden. Construct validity was measured with exploratory factor analysis with Varimax rotation. This resulted in three factors for the "physical set", five factors for the "psychosocial set" and four factors for the "follow-up set" with strong factor loadings and a total explained variance of 62-77.5%. Thirteen questions in the SF-36 were used for concurrent validity showing Spearman's r(s) 0.3-0.6 in eight questions and less than 0.2 in five. Test-retest was used for stability reliability. In set follow-up the correlation was strong to moderate and in physical and psychosocial sets the correlations were moderate to fair. This may have been because the physical and psychosocial status changed rapidly during the test period. All three sets had good homogeneity. In conclusion, the 3-set 4P showed overall acceptable results, but it has to be further modified in different cultures before being considered a fully operational instrument for use in clinical practice.