Idiographic measurement of depressive thinking: development and preliminary validation of the Sentence Completion Test for Chronic Pain (SCP)

Abstract

Abstract Background and aims Depression is a common feature of chronic pain, but there is only limited research into the content and frequency of depressed cognitions in pain patients. This study describes the development of the Sentence Completion Test for Chronic Pain (SCP), an idiographic measure for assessing depressive thinking in chronic pain patients. The sentence completion task requires participants to finish incomplete sentences using their own words to a set of predefined stems that include negative, positive and neutral valenced self-referenced words. In addition, the stems include past, future and world stems, which reflect the theoretical negative triad typical to depression. Complete responses are coded by valence (negative, positive and neutral), pain and health-related content. Methods A total of 89 participants were included in this study. Forty seven adult out-patients formed the depressed pain group and were compared to a non-clinical control sample of 42 healthy control participants. This study comprised several phases: (1) theory-driven generation of coding rules; (2) the development of a coding manual by a panel of experts (3) comparing reliability of coding by expert raters without the use of the coding manual and with the use of the coding manual; (4) preliminary analyses of the construct validity of the SCP. The internal consistency of the SCP was tested using the Kuder-Richardson coefficient (KR-20). Inter-rater agreement was assessed by intra-class correlations (ICC). The content and construct validity of the SCP was investigated by correlation coefficients between SCP negative completions, the Hospital Anxiety and Depression Scale (HADS) depression scores and the number of symptoms on the Structured Clinical Interview for DSM-IV-TR (SCID). Results As predicted for content validity, the number of SCP negative statements was significantly greater in the depressed pain group and this group also produced significantly fewer positive statements, compared to the healthy control group. The number of negative pain completions and negative health completions was significantly greater in the depressed pain group. As expected, in the depressed pain group, the correlation between SCP negatives and the HADS Depression score was r=0.60 and the correlation between SCP negatives and the number of symptoms on the SCID was r=0.56. Conclusions The SCP demonstrated good content validity, internal consistency and inter-rater reliability. Implications Uses for this measure, such as complementing questionnaire measures by an idiographic assessment of depressive thinking and generating hypotheses about key problems within a cognitive-behavioural case-formulation, are suggested.