Sample Data
- It is usually difficult to measure every unit in a population.
- So you get measurements on all units in a sample.
- But the sample needs to be representative of the population. So we can make a generalization on the population.
- Types of Samples
Issues with Collecting Sample Data
- Collecting sample data is expensive (time and money).
- Data might be biased:
- Selection Bias
- What if the sample isn't representative of the population?
- Nonresponse Bias
- What if participants refuse to cooperate?
- Measurement Error Bias
- What if the response from a unit is measured incorrectly?
- Ideal to get a Random Sample