Algebra 2 / Unit 10: Statistics and Data Analysis
10.4 Sampling Methods and Bias
Notes
A population is the whole group you want to know about. A sample is the part you actually study.
- Simple random sample: every group of that size is equally likely to be chosen.
- Stratified: split into groups (strata), then randomly sample from each.
- Cluster: split into groups, randomly pick whole groups.
- Systematic: pick every $k$th member from a list.
- Convenience and voluntary response samples are usually biased: they don't represent the population.
- Question wording can also cause bias.
Practice
A store surveys every 10th customer who walks in. What kind of sample is this?
Picking every $k$th member is systematic sampling.
A website asks visitors to vote in an online poll. What is the main problem?
People choose whether to respond, so the results don't represent everyone.
A principal randomly picks 25 students from each grade level. What kind of sample is this?
Grade levels are the strata, and each is sampled randomly.
Ready for more? Take the Unit 10 test.