1. Selecting Research Participant

2. Sample & Population
A population is the entire set of individuals of interest to a researcher.
A sample is a set of individuals selected from a population and usually is intended to represent the population in a research study.

3. Some Terms
A biased sample is a sample with different characteristics from those of the population.
A representative sample is a sample with the same characteristics as the population.
Selection bias or sampling bias occurs when participants or subjects are selected in a manner that increases the probability of obtaining a unrepresentative sample.

4. Sample Size
The first principle is that a large sample is probably more representative than a small sample. Although large samples are good, there is also a practical limit to the number of individuals that is reasonable to use in a research study.

5. Sample Size
Although a sample size of 25 or 30 individuals for each group or each treatment condition is a good target, other considerations may make this sample size unreasonably large or small.
It can be computed that for a population of 100,000 or more the sample must have at least 384 individuals to be confident that the preferences observed in the sample are within 5% of the corresponding population preferences.

8. Sampling Basics Sampling methods fall into two basic categories:
probability sampling (5 types)
nonprobability sampling.(2 types)

9. 33%White
33%Black
33%Latino
60% White,
10% Black,
30% Latino

10. Random schools Snowball sampling?
33% available White 33% available Black 33% available Latino
Snowball sampling?