What Is Sample Size?
Sample size is how many people, items, or observations a survey or experiment needs to draw a conclusion with a chosen level of confidence and margin of error. Larger populations, higher confidence levels, and smaller margins of error all push the required sample size up. Using too small a sample risks a result that doesn't reflect reality; too large wastes time and money.
Example
Surveying a population of 10,000 people with a 95% confidence level and a 5% margin of error requires a sample of about 370 people — sample size requirements level off quickly, so a population of 50,000 would need a similar sample.