The data was obtained from the US Census Bureau website.
The US Census Bureau provides population data for countries according to years. The data is available in a Comma Separated Value (CSV) format and readily available for download. From the CSV, the Total population for each country, and the conscious population (above 12 years) for each country per year is obtained.
The average death rates for each country were obtained from the World Bank website. Subtracting the average death rate from each year's conscious population gives the conscious population for the successive year.