Why do sampling?
(go to Outline)
Sampling is done because you usually cannot gather data from the entire population. Even in relatively small populations, the data may be needed urgently, and including everyone in the population in your data collection may take too long.
A survey without sampling
Population of Papua New Guinea (2000 census):
726,680 children less than 5 years of age
1,298,503 women 15-49 years of age
If one survey team could collect data on 13 women and 13 children per day, 6 teams would take 16,648 days or 45.6 years to complete data collection. (And that does not allow for any travel time or rest days for the survey workers.)
If you had the money and time, would these data be useful?