The Manitoba Population Health Research Repository contains records of all physician contacts in hospitals and in offices for the total population of Manitoba. A comprehensive population registry facilitates record linkage using a scrambled personal health identification number (PHIN), unique for each individual. To maintain the anonymity and confidentiality of survey participants, Manitoba Health used the survey identifiers of name, birth date and address to find the PHIN for 2479 of the survey participants (83.2%). Manitoba Health removed personal identifiers from the survey file and scrambled the PHIN to permit linkage to the Research Repository.
The day of completing the questionnaire was considered to be the reference day for determining the respondent’s age and the five-year interval before the questionnaire. For this period, divided into one-year segments, all physician contacts for the following International Classification of Diseases, ninth revision (ICD-9) codes were identified: asthma (ICD-9 code 493), bronchitis not otherwise specified (ICD-9 code 490), chronic bronchitis (ICD-9 code 491), emphysema (ICD-9 code 492) and chronic airflow obstruction (ICD-9 code 496).
Kappa coefficients were calculated to determine the agreement between survey responses and physician contacts documented in the database for periods from one to five years before the survey. Sensitivity and specificity of the administrative data were estimated considering response to the questionnaire as the gold standard.
The study was approved by the Ethics Board of the University of Manitoba and the Access and Confidentiality Committee of Manitoba Health (Winnipeg, Manitoba).