The PCQ was developed specifically for patients undergoing addiction treatment. The PCQ includes six subscales (Self, Family, Legal, Finance, Health, and Work). Five out of the six subscales measure external coercion to participate in a substance-abuse treatment programme. The sixth subscale, Self, measures an internal form of perceived coercion or pressure. For example, item #1 is, ‘I feel pressure to participate in this drug/alcohol treatment programme…because I know that I’m an addict/alcoholic and that I need rehab to get off drugs/alcohol,’ and #3 is ‘I feel pressure to participate in this drug/alcohol treatment programme…because I feel horrified and ashamed of the person I have turned into’. The PCQ instrument contains 30 items that are presented in the form of statements (see Additional file 1). Respondents rate each statement with a 5-point scale (1, strongly disagree; 2, somewhat disagree; 3, neither agree nor disagree; 4, somewhat agree; 5, strongly agree). A higher score implies a greater degree of coercion perceived by the respondent . Klag et al. (2006) reported that the PCQ has acceptable divergent validity. The validity was demonstrated by a negligible relationship between the PCQ and a presumably unrelated measure (i.e., a measure of spirituality), where the overall r was 0.04 and r values for PCQ subscales were 0.03–0.10) . A previous analysis of PCQ reliability indicated that the subscales showed adequate internal consistency (Cronbach’s alpha: 0.66–0.87) and good total internal consistency (Cronbach’s alpha: 0.87) . To validate the PCQ in the new setting, we undertook an exploratory factor analysis. First, three items were removed from the PCQ, based on a pre-test of the scale and the notion that these items seemed irrelevant in a Norwegian setting (see Additional file 1). We proceeded to examine whether the remaining items yielded a factor structure similar to that of the original version and whether each item had sufficient factor loadings on its respective subscales. The analysis included principal axis and oblique rotation methods (promax). Kaiser’s eigenvalue-greater-than-one rule was used to determine the number of factors . To ensure internal validity for the present study and to obtain the most parsimonious model, problematic items were removed when they had low factor loadings (<0.4)  or did not work as intended. As a result of this analysis, we removed two items in the health subscale. One item was removed, because it represented an extra (seventh) subscale, which constituted a single item only (probably an overfactoring issue: this scale barely exceeded the eigenvalue-of-one criteria). The other item was removed, because it had a low factor loading (see Additional file 1). After these amendments, the scale factors were similar to those in the original scale, and all items had factor loadings > 0.4 on their respective subscales. Based on the PCQ scale results, we divided the patients into two groups: patients that did not perceive any form of coercion and patients that perceived some form of coercion (agreed or strongly agreed) on one or more of the subscales.