1. Sample Surveys
Chapter 11

2. Sampling
Goal: Learn about the parameters of a population that largest enough that it is impossible or impractical to measure.
To accomplish this we take a representative sample and use it to draw conclusions about the population.

3. Bias
A sample that does not represent the population in some important way is biased.
Any sample that systematically under or other represents a section of the population is biased.
Random selection of the individuals in the sample is the best remedy for bias.

4. Sample Facts
The size of a population is not relevant to the reliability of the sample.
The sample size is the most important factor in the reliability.

5. Terms Census: A sample that includes the entire population.
Parameter: A trait of a population. Its mean and standard deviation of the population are parameters.
Statistic: Calculated values that summarize a sample. Statistics are usually used to estimate population parameters.

6. Parameters vs Statistics
If statistics from a sample accurately reflect the parameters of the population it is said to be representative.

7. Simple Random Sample
A SRS is one in which every possible sample of a given size has an equal chance of being selected.
A sampling frame is a list of all of the individuals from which the sample is drawn.

8. Terms II
Sampling Variability: The different results we obtain when more than one sample is drawn. It is the difference between samples.

9. Sampling Designs
Stratified random sample: the population is divided into homogeneous groups called strata and then a SRS is taken from each strata.
Forces representation different groups.
Use when there are different groups within a population that might have react differently.

10. Sampling Designs II
Cluster Sampling: the population is made up of heterogeneous groups. Randomly select group(s) and take all.
Multistage Sampling: Sampling methods that combine more than one sampling method.
Systematic Sampling: using a rule to select a sample. Use when the order of the list will have no effect on the responces.

11. Types of Bias Voluntary Response: Self selected sample. Volunteers
Convenience Sampling: sample the individuals that are easy or nearby.
Undercoverage: lack of representation of a section of the population.
Nonresponse bias: Selected members of the sample do not reply.
Response bias: Anything that influences the responses. For example: leading questions