AP Stats: Unit 4 (experiments)

Observational Study

A study that does not attempt to alter the behaviors of participates. Outcomes are simply measured (observed)

Experimental Study

Study in which a treatment (or multiple treatments) is applied. The explanatory variable is manipulated in order to measure a response.

Convenience Sample

A researcher gathers data that is easy to obtain

Systematic Sample

A researcher collects data from every n^th individual available

Stratified Sampling

A researcher collects data randomly from different categories (or “strata”) for equal or proportional representation

Clustered Sampling

A researcher randomly selects several “clusters” of individuals, and all members of the selected clusters are in the sample. 

Simple-Random Sample (best in most cases)

All members of the population are equally likely to be included in the sale and all groupings are possible

Bias in stats

A systematic over or under estimation of the value of a parameter

Parameter

Population value → Standard dev, mean, etc

Undercoverage Bias

Certain indiduals or groups are excluded from the sampling methodi

Non-response Bias

Individuals are selected for a sample but do not (or cannot) produce a response

Voluntary-response Bias

Members of a population selected themselves to contribute a response

Response bias

A response given by a member of the sample, but it is incorrect in some way (a lie, influenced by interaction, misunderstanding, etc.)