Surviving Rectal Cancer at the Cost of a Colostomy International Validation of the Colostomy Impact Score

This retrospective cohort study has three main aims: 1) To identify demographic and socioeconomic factors influencing stoma impact and HRQoL, 2) To asses reliability and to validate the translated and cross-cultural adapted CI score internationally in multiple different centres, across a variety of patient groups and across cultural, religious, socioeconomic and physical borders and 3) To investigate if differences in everyday stoma care and -costs across countries and cultures affect CI or HRQoL.

International validation will be conducted as a retrospective cohort study on patients with a permanent colostomy after curative intended surgery more than 12 months prior to inclusion. Local health care professionals will identify includable patients and register relevant clinical information on each patient from the hospital chart. Most centres will include patients from national or regional databases, some will however include conveniently if a database is not available. Our international collaborators will be responsible for sending out and collecting the questionnaires and returning the completed questionnaires to the undersigned. In countries with sufficient internet accessibility and -infrastructure the data collection will be web based i.e. patients are sent a link to the redcap-database for them to enter their answers directly. Some centres will employ paper versions of the questionnaires. In areas with substantial number of illiterates investigator led interviews can be performed.

As the CI-score is a construct based on a formative model, statistical analysis based on the Classical Test Theory(CCT) and Item Response Theory (IRT) cannot be applied. However, the following aspects of validity and reliability from the Consensus-based Standards for the selection of health Measurement Instruments (COSMIN) checklist15-17 can and will be evaluated:

Content validity: Comprehensiveness and relevance of the questions in the CI-score have been ensured with the way of the development of the CI-score with the starting point in a Basic Stoma Questionnaire developed by an expert group supplemented by patients ensuring that all possible factors affecting stoma function/impact was included before regression analysis lead to the seven weighed questions1. After translation and cross-cultural adaptation face-validity of each translated CI-score will be assessed again by the collaborators before inclusion of patients.

Construct validity: This will be tested with hypothesis-testing. Hypotheses regarding mean differences and expected correlations between scores of instruments are formulated a priori. Hypotheses on how the CI-score and HRQoL are related to other factors are formulated a priori. For convergent validation the CI-score will be tested against 5 anchor questions (not validated) and the EORTC QLQ C30+ the colorectal specific CR29 (validated). Cross-cultural validity: See translation section.