Advances and Applications in Statistics
Volume 10, Issue 2, Pages 219 - 235
(December 2008)
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THE SEASONALITY OF BIRTH IN URBAN SOUTHWESTERN NIGERIA
O. I. Shittu (Nigeria), T. A. Oyeniyi (Nigeria) and T. O. Olatayo (Nigeria)
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Abstract: This paper focuses on the study of differences in the seasonality of birth between the rural and urban dwellers in the southwestern Nigeria. Harmonic analysis is carried out on data assuming the period (or cycle length) is known a priori to determine the time of the year when number of births is peaked and the spectrum analysis is also used assuming the period is unknown a priori to determine the interval of occurrence of such peak. Fisher’s exact test is used to test the Fourier frequencies corresponding to the observed peaks in the periodogram in order to determine the most prominent period in the series.
The results show that seasonality of birth in the urban area that peaked in May-June in the southwestern part of Nigeria, while it peaked in the rural area between April-May of the year (Ayeni [2]). The magnitude of variation of 18% is however significantly higher than (7%) in the rural area. The periodogram analysis also shows that peak will be occurring at intervals of twelve months in the urban area. Assuming a 40-week gestation period, it can be inferred that conception mostly occurs around September to late October that are generally the coolest months of the year, which encourage more mating, hence more conception. The results agree with the reports from Australia in the USA (Mathers and Harris [11]), Czech Republic (Bobak and Gjonca [4]) and Haryana in India (Anand et al. [1]). |
Keywords and phrases: seasonality, harmonic analysis, spectrum, periodogram, gestation. |
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