Psychometric evaluation of the Patient Assessment of Chronic Illness Care instrument using Item analysis according to the Rasch model.

The Patient Assessment of Chronic Illness Care (PACIC) instrument assesses patient care in alignment with the chronic care model. The aim of the study was to comprehensively validate the PACIC using the Rasch model. A special focus was placed on the investigation of local dependence (LD), differential item functioning (DIF) and targeting. This secondary analysis utilized data of 760 patients with a diagnosis of diabetes who had participated in the Swiss CoDiab-VD cohort study. The psychometric properties of the French PACIC-version were evaluated using the Rasch model. DIF was investigated in relation to age, gender, education, year of recruitment into the CoDiab-VD cohort study, type of diabetes and whether patients got an injectable antidiabetic drug or not. The initial analysis of the PACIC revealed poor fit to the Rasch model (χ <sup>2</sup> -p < 0.001) with response dependency being the most prominent problem. After combining the items into two testlets (testlet 1: Items 1-11; testlet 2: Items 12-20), good overall model fit was found (χ <sup>2</sup> -p = 0.77) as well as good reliability (Person Separation Index = 0.85) and targeting. DIF with regard to whether patients got an injectable antidiabetic drug or not was found for testlet 2. However, the size of this DIF was regarded as not being substantial. The PACIC is a well-targeted, reliable unidimensional instrument to assess patient care in alignment with the chronic care model in patients with diabetes. It is free of substantial DIF. The PACIC-20 sum score can hence be used in clinical practice for individual diagnostic. For evaluation purposes like assessment of change or group evaluations, the usage of the interval-scale level person parameters is recommended as it permits using parametric statistical analyses and provides a more accurate picture about the actual amount of change