Statistics & Probability
Random Sampling
A sample is a subset of a population used to make inferences about the whole population. Key concepts: • Population: The entire group being studied • Sample: A smaller group selected from the population • Random sample: Every member has an equal chance of being selected • Biased sample: Some members are more likely to be selected Good sampling methods: • Simple random sampling • Systematic sampling (every nth person) • Stratified sampling (divide into groups, sample from each) Poor sampling methods: • Convenience sampling • Voluntary response sampling
Example:
To find the average height of 7th graders in a school with 300 students: Good method: Randomly select 30 students from the complete list Poor method: Only measure students on the basketball team (biased - likely taller) The random sample will give a better estimate of the true average.