Pearl’s curves which have been copied in this report (Charts II to VII) enable us to follow his conclusions. Pearl offers a partial explanation for the variations in the different cities. There can be no doubt but what many factors play a role in the causation of these variations, and it is to be regretted that up to the present no statistics for smaller, more homogeneous communities have as yet been reported which could be compared with Pearl’s excellent work on the large cities of the country. Were his work supplemented by records from smaller towns in which the varying factors are less numerous, in which there is less occupational variation, additional conclusions could probably be reached. The unfortunate feature is that as a rule statistics from the smaller cities and towns are less reliable.
From a detailed mathematical study of influenza in 39 of our largest cities, done chiefly by the means of multiple correlation, with the hope of being able to explain the differences in the epidemic curves of weekly mortality in the various cities, Pearl concludes as follows:
“The general conclusion to which we come from an examination of the correlation data assembled to this point is that these four general demographic factors, density of population, geographical position, age distribution of population, and rate of recent growth in population, have practically nothing to do, either severally or collectively, with bringing about those differences between the several cities in respect to explosiveness of the outbreak of epidemic mortality in which we are interested. Significantly causal or differentiating factors must be sought elsewhere.”
CHART II.
Death rates from all causes by weeks in certain large cities of the United States during the winter of 1918–19. (Pearl.)
CHART III.
Death rates from all causes by weeks in certain large cities of the United States during the winter of 1918–19. (Pearl.)
CHART IV.