Producing Data Chapter 5

Observational Study Observes individuals and measures variables of interest but does not attempt to influence the responses

Experiment Deliberately imposes some treatment on individuals in order to observe their responses

Statistical Inference Answers specific questions with a known degree of confidence

Designing Samples Section 5.1

Population The entire group of individuals that we want information about

Sample Part of the population that we actually examine in order to gather information

Sampling Involves studying a part in order to gain information about the whole

Census Attempts to contact every individual in the entire population

Sample Design Refers to the method used to choose the sample from the population

Types of Sample Design

Voluntary Response Sample Consists of people who choose themselves by responding to a general appeal Usually bias

Convenience Sampling Chooses the best individuals easiest to reach

Bias Systematically favors certain outcomes

Simple Random Sample Each individual in a population has an equal chance to be selected into a sample

Table of Random Digits Long string of digits 0 thru 9 with 2 properties: Each entry in the table is equally likely to be any of the 10 digits Entries are independent of each other

Probability Sample A sample chosen by chance Need to know what samples are possible and what chance, or probability, each possible sample has

Note: The use of chance to select the sample is the essential principle of statistical sampling

Stratified Random Sample Divide the population into groups of similar individuals, strata Choose a separate SRS in each stratum Combine the SRSs to form the full sample

Undercoverage Occurs when some groups in the population are left out of the process of choosing the sample

Cautions About Sample Surveys

Nonresponse Occurs when an individual chosen for the sample cannot be contacted or does not cooperate

Wording of Questions Most important influence on the answers given to a sample survey

Note: Large random samples give more accurate results than smaller random samples

Practice Problems pg. 285 #5.19-5.30