AP Stats Unit 4 - Sampling

Convenience Sample

Choosing a sample that is readily available in a non-random way. Ex: Asking for a volunteer

Simple Random Sample (SRS)

Choosing a sample by randomly selecting individuals from the population. Each possible sample has an equal choice (probability) of being chosen. Ex: Gave population numbers, chose random numbers

Stratified Sampling

When your population is divided into homogeneous groups by some characteristic and then a SRS is taken from each group. Ex: A population is given one of four colors, then an SRS is taken.

Cluster Sample

When your population is divided into heterogenous groups called clusters. Some of the clusters are randomly chosen and everyone in those clusters is in your sample. Ex: Took population and grouped by location, then randomly chose one of the locations.

Systematic Sampling

When you randomly choose a starting point from your population and then select a sample using a fixed interval based on your population. Ex: Lined population up, (name) is chosen and then every fourth person was asked a question.

Voluntary Response Bias

When people choose to be in a sample. Usually occurs with a Convenience Sample

Undercoverage

When some members of the population cannot be chosen or are very unlikely to be chosen.

Non-Response Bias

When an individual is selected to be in the sample, but they choose not to participate or cannot be reached after being chosen.

Response Bias

When there is a pattern of inaccurate responses. This could be due to the wording of the question, the interviewer, individuals lying for some reason, etc.