A modified cohort method for secular trend analysis: heart disease mortality in the USA 1914-1963 and follow-up to 1983.
The principles behind the analysis of secular trends of cause-specific mortality rates by 'current' and 'cohort' methods were subjected to theoretical examination. A more general method, named here the 'midpoint' method, was found for which the 'current' and 'cohort' methods are special types of limiting cases. It is shown that the span of time over which the causes of disease act, and the period of life, whether early or late, in which they are predominantly concentrated will determine which of these three methods is appropriate for each specific cause of death. For 'cumulative' diseases (of which atherosclerosis and hypertension are thought to be examples), defined as diseases which accumulate slowly over the greater part of a lifetime under the influence of etiologic factors that are widely dispersed in time, the data favor the 'midpoint' method as the most appropriate one of the three. Secular trends in diseases of the heart in the USA from 1914 - 1963 were examined in 1968 by this method, thus generating predictions about the trends to be expected after 1963. Although no definitive conclusion could be reached at that time, the probabilities then favored the hypothesis that the etiologic forces which contribute to heart disease mortality reached a peak around 1930 or earlier, and that the subsequent decline had not yet given evidence of ending. Predictions of secular declines in mortality rates attributed to diseases of the heart made in 1968 are compared here with the subsequent 20 years of experience by specific age-race-sex groups. Validation of the midpoint cohort method of analysis is claimed. The peak in heart disease mortality that occurred in 1968 is seen as a temporary fluctuation within the grand pattern of 20th Century USA.
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Department of Pathology, Louisiana State University, Medical Center, New Orleans 70112.
D000328:Adult; D000368:Aged; D015331:Cohort Studies; D003627:Data Interpretation, Statistical; D005260:Female; D006331:Heart Diseases / Q000401:mortality*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D013997:Time Factors; D014481:United States / Q000453:epidemiology