Peak amplitude in Nigeria is above 30 percent while US peak amplitude is 6 percent. Vertical lines represent 95 percent confidence intervals. For many SSA countries, observed fluctuations in monthly birth amplitude can be represented by a sinusoidal function, as illustrated for Nigeria. Source: Annual summary of Monthly Vital Statistic Report, National Center for Health Statistics, United States; http://www/cdc.gov/nchs/bir… Accessed 2010 June 21. Nigeria Demographic Health Surveys.