Mortality in co-morbidity (I)--Analysis of the results in the Multiple Medical impairment Study for impairments with elevated blood pressure as the second or co-morbid impairment

Abstract

Background: In life insurance medicine as in general medicine, it has long been recognized that chronic medical conditions often occur in persons, not as a single impairment or risk factor, but as multiple co-morbid conditions. Nevertheless, it was not until 1999 that the first intercompany Multiple Medical Impairment Study (MMIS) was completed by Harry A. Woodman, FSA. Prior intercompany mortality studies from 1903 to 1983 had been almost 100% devoted to single impairments excluding all comorbid impairments except minor ones with a mortality ratio (MR) of 125% or less. However, abundant co-morbid mortality data have been presented in other clinical and single company studies. Examples are in the studies on diabetes mellitus abstracted in the 1976 Medical Risks monograph and two more recent studies. In this article, we analyze overall mortality and mortality for most of the individual impairments with elevated blood pressure (EBP) as the co-morbid impairment, provided that exposures and deaths were sufficient in number to utilize.

Methods: From the standardized results page for the impairments published in the MMIS, we have extracted 3 tables of aggregate mortality experience on groups with a single impairment, 2 impairments, and 3 impairments. Then we prepared a similar table from the substandard experience of the 1979 Blood Pressure Study. Weighted mean age was calculated, for all groups, and excess death rates (EDRs) in the group with EBP were adjusted to the mean age of the 2-impairment group. Next a subsidiary table was prepared of data from 57 impairments in Section III of the MMIS. The data included the name of the impairment, exposures, observed and expected deaths (d and d'), overall EDR as a multiple and as a single impairment, and as a co-morbid impairment with EBP as the second impairment. The age-adjusted EDR for EBP alone was added to the EDR as a single impairment, and the sum was compared with the co-morbid EDR for the impairment and EBP. The 57 impairments were then divided into 3 groups (Tables 4-6), depending on whether the comorbid EDR exceeded the sum of the separate EDRs, was less than the sum, or approximately equal to the sum.

Results: EDR rose with decennial age group in each of the 4 groups shown in Table 1. Mean annual EDR, all ages combined, increased from 2.6 per 1000 for a single impairment to 5.2 for 2 impairments to 9.2 for 3 impairments. In males in the 1979 Blood Pressure Study, the mean EDR, all rated policies combined, was 5.0 per 1000, and the mean rate of increase per decennial age group was 2.77 per 1000, aged 20-29 to 60-69. In 18 of 57 comparisons, the co-morbid EDR exceeded the sum of the separate EDRs by 1.0 or more; in 20 the 2 EDR values were approximately equal, within +/- 0.9; and in 19 the co-morbid EDR was less than the sum of the separate EDRs by 1.0 or more. In Table 4, we listed the 18 impairments whose co-morbid EDR exceeded the sum of the separate EDRs, entering the overall co-morbid mortality data (combined impairment and EBP), and the comparison EDRs. The mean co-morbid EDR was 11.3 per 1000 per year, with a range from 6.8 to 17.7; the mean sum of EDRs was 8.3 per 1000 (range 5.6 to 12.5). The mean excess EDR was +2.8, with a range from +1.2 to +9.2. Results are shown in Tables 5 and 6 for the groups in which the co-morbid EDR was less than or approximately equal to the sum of the separate EDRs.

Conclusion: In 18 of 57 comparisons made in MMIS, there was a synergistic excess mortality when the co-morbid EDR (impairment with EBP as second impairment) was compared with the summated EDR of the impairment alone and the EDR for EBP alone. In the remaining 68% of the impairments, the co-morbid EDR was approximately equal to or less than the sum of the separate EDRs.