[Analysis on birth time of 4636 babies with circular distribution method in Shijiazhuang prefecture]

The study adopts circular distribution method and periodic regression technology with cosine curve to make statistic analysis. According to the result of the statistic by season, among 4,636 babies of natural parturition from 1985 to 1988, the angle even value is 272.91 degrees, a = 0.05, by evenness examination, which indicates the tendency of concentration. The further periodic regression analysis gives out an equation: ŷ = 289.75 + 48.68 cos (wti-272.91), determination coefficient R2 = 0.56, and variance analysis concludes F = 8.35, P less than 0.01. The fitting result is satisfied, which points out that the birth time season waves in a year's period and the birth rate is high in winter. While the statistic by month, the angle even value is 338.40 degrees, a = 0.01, ŷ = 96.58 + 19.82 cos (wti-338.40), R2 = 0.42, F = 15.28, P less than 0.01, which still indicate that the birth time has a year's periodic fluctuation, with its peak on December 8. As for the statistic by day in each month, the angle even value is 213.86 degrees, evenness examination P greater than 0.05, indicating no monthly periodic fluctuation and no peak on 1st and 15th of lunar year, while the statistic by birth o'clock in a day, the angle even value is 117.31 degrees, P greater than 0.05, no day and night rhythm.