A statistical analysis of the annual pattern in black and white births in the Southeastern and Midwestern USA, 1969 thru 1976

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Abstract
The annual pattern of black and white births in the Southeastern and Midwestern United States was analyzed for the years 1969 thru 1976. Monthly means for the eight‐year period were obtained individually for 17 states and for black births in the District of Columbia. The states and the district were selected for their large black populations and represent approximately 70% of black births in the USA. The data were analyzed in two ways, with an analysis of variance (the two‐factor mixed design with repeated measures on one factor) and by comparing the confidence intervals for the least‐squares derived Fourier coefficients of a sine curve. In addition, the range was compared between regions and between races and related to latitude. The analyses of variance indicated that statistically significant differences existed between regions and between races. The cosinor‐like method failed to adequately represent the data in most cases. The completely urban black population in the District of Columbia exhibited an annual pattern that was similar to the pattern in neighboring states, states that contained large rural populations. The range in the monthly averages of births was different between regions and between races, and inversely correlated with latitude (with “North”; and “white”; having smaller ranges). Some possible causative factors are briefly reviewed, and the correlation of sperm counts and conceptions offered as a new possibility.