Population
- Individuals/units/cases
- the objects on which a measurement is made
- population
- the set of all individuals or units of interest to an investigator.
- parameter
- a numerical characteristic of a population
- sample
- a subset of individuals or units selected from the population
- statistic
- a numerical characteristic of a sample
Sampling Methods
- simple random sampling
- a way of drawing an unbiased sample from a population
- A simple random sample of size n is a sample drawn in such a fashion that each possible sample of size n had the same chance of being selected
- implication = every member of the population has the same chance of being selected
- n/N = sample size / population size
- typically drawn without replacement
- a member of the population cannot appear in the sample more than once
- stratified random sampling
- in a population with subgroups, where individuals in the subgroups are more similar to each other
- divide the population into the subgroups (strata) and draw SRS (simple random samples) from each subgroup
- the use mathematical techniques to combine the information from different stratas
- cluster sampling
- population is divided into clusters in such a way that it is easier to sample clusters of individuals rather than the individuals themselves
- systematic sampling