A survey team in Srilanka conducted a health survey in a village by dividing the population of the village in three different age ranges. The first range consisted of the population aged between 0 to 20 years, the second range was of the population above 20 years and below 45 years, and the last range was comprised of all the villagers above 45 years of age. A sample was drawn from each range according to the proportion of that range. The results showed that the healthiest people were between the age 0 and 20 years. Identify the type of sampling technique used by the survey team.