Mon, March 20, 2017, noon:
Dean Yang, Taken by Storm
Introduction: Despite our ability to breed continuously, almost all human populations exhibit seasonal variation in reproduction. Knowledge of these seasonal birth patterns gives insight into drivers of human fertility, the influence of birth month on later life outcomes, and can help us characterize the seasonal dynamics of many childhood infectious diseases. Seasonality of births has been extensively studied in North America, Europe, and East Asia but less so in African settings. This paper is the first to systematically test for and document birth seasonality in Sub-Saharan Africa (SSA).
Data and Methods: Birth data from Demographic and Health Surveys are aggregated by country and ecological zone. The monthly time series of births are then de-tended and converted to monthly amplitude. Amplitude is defined as the percent deviation from the annual monthly mean. We then calculate the periodicity of the monthly birth amplitude time series using Fourier spectral analysis. We also measure seasonality using Ordinary Least Square regression.
Results: We find that births are indeed seasonal with a few exceptions. However we find large variation in the amplitude (from five percent to 65 percent) and pattern (unimodal, bimodal . . . ) across regions. We also look at birth seasonality across ecological zones. Finally where possible we disaggregate the data and look at birth seasonality across maternal characteristics such as mother's education level, type of residence (e.g., rural or urban), and religion.
Country of focus: Sub-Saharan Africa.