Validity of cerebrovascular disease mortality statistics in Bulgaria

Background. Cerebrovascular disease (CVD) is the leading cause of death in Bulgaria but the increasing mortality could be explained by inaccuracy of the statistical data and so investigation of the validity of CVD mortality statistics is of primary importance. Methods. The investigation comprised three phases. An adequate questionnaire, requiring a reliable decision on the presence/absence of CVD in deceased patients was developed. During the first phase the questionnaire was validated on the basis of 325 inpatients aged 20 years and over. In the second phase the applicability of the questionnaire was proved and verified in patients who died outside hospital. This was performed by using 'twin'-copies of each questionnaire, completed in the first phase. In the third phase the applicability of the questionnaire for evaluation of CVD mortality statistics was checked using a sample of 119 death certificates. Statistical analysis of the information from each of the three phases was intended to evaluate the sensitivity and specificity of the questionnaire and to assess the validity of mortality statistics. Results. High sensitivity of the questionnaire was established and it remained at the same value during each of the th ree phases of the study. Specificity was considered lower when the questionnaire was applied for those who died outside hospital and when used by non-neurologists. An underestimation of CVD by 8.9% was obtained in the first phase and it amounted to 37.81% in the third phase. A high proportion of incomplete or unsystematically completed death certificates was found. This represents a potential source of inaccuracy in mortality statistics. Conclusion. The questionnaire developed for presence/absence of CVD in deceased patients proved to be a reliable instrument for certifying CVD mortality.