Integrated Math 3 / Unit 8: Statistics and Inference
8.3 Sampling and Bias
Notes
A population is the whole group of interest. A sample is the part you actually measure. A good sample is representative.
- Simple random sample: every member has an equal chance of being chosen.
- Stratified sample: split into groups (strata), then sample randomly from each group.
- Biased methods include convenience samples and voluntary response samples (people choose to respond).
- Bias comes from how the sample is chosen, and a bigger biased sample is still biased.
Practice
A school wants to know student opinions on lunch. Which method is a simple random sample?
Every student has the same chance of being chosen.
A radio show asks listeners to call in and vote on a new city park. Why are the results likely biased?
Voluntary response samples overrepresent people with strong feelings.
A school has 40% freshmen, 30% sophomores, 20% juniors and 10% seniors. To survey 100 students with a stratified sample, how many sophomores should be chosen?
Each grade should appear in proportion to its share of the school: 30% of 100 is 30.
Ready for more? Take the Unit 8 test.