Temporal variations in mortality: a comparison of U.S. suicides and motor vehicle fatalities, 1972-1976.

Among the various types of mortality, motor vehicle fatalities (MVF) and suicides are two that are very responsive to social, economic, and psychological factors. The analysis of the temporal patterns of suicides and MVF points to important but neglected forces affecting them. This paper examines the daily patterns of MVF and suicides for the United States from 1972 to 1976. The effects of the day of the week, month, year, and holidays on these types of mortality are estimated. Total MVF and suicides, as well as daily differentials by sex, age, and race, are analyzed with regression techniques. The results show that temporal variations are stronger in MVF than in suicides but are present in both. MVF tend to peak on Saturday, in the summer months, in 1972 and 1973, and on holidays. Suicides are generally highest on Monday, in the spring months, in 1975 and 1976, and on nonholidays. Differentials in the temporal patterns are evident. For instance, whites generally have a sharper decline in suicides on holidays than do nonwhites. The holiday peak in MVF for the 60 and over population is Christmas, while it is New Year's for the younger age groups. Males exhibit a greater increase in suicides from March to May than do females. Finally, the results of a comparison of the daily patterns of MVF and suicides revealed a negative correlation. This contrasted with the strong positive relationship between MVF and suicides generally found in cross-sectional studies. The implications of these findings are briefly discussed.