STATS: Modeling the World, Chapter 12:Sample Surveys : Terms and Formulas

Population

The entire group of individuals/instances about whom we hope to learn

Sample

A (representative) subset of a population, examined in hope of learning about the population.

Sample Survey

A study that asks questions of a sample drawn from some population in the hope of learning something about the entire population

Bias

Systematic failure of sampling method to represent its population; over/underestimates parameters- almost impossible to recover from it, common errors include relying on voluntary response, undercoverage of the population, nonresponse bias, and response bias

Randomization

Best defense against bias; each individual is given a fair, random chance of selection

Sample Size

Number of individuals in a sample; determines how well the sample represents the population, not the fraction sampled

Census

Sample that consists of entire population

Population Parameter

Numerically valued attribute of a model for population; rarely expect to know the true value but an estimate can be made

Sample Statistic

A sample of calculated data

Representative

If the statistics are computed from a sample and reflect the corresponding population parameters

Simple Random Sample (SRS)

Sample in which each set of elements in the population has an equal chance of selection

Sampling Frame

List of individuals from whom the sample is drawn; individuals who may be in the population of interest but are not included in this are not in any sample

Sampling Variability

Natural tendency of randomly drawn samples differ from each other, either because they should or there is error

Stratified Random Sample

Sampling design in which population is divided into strata (several subpopulations), and random samples are drawn from the stratum; if they are homogenous but are different from each other, this yields more consistent results than an SRS

Cluster Sample

Sampling design where entire groups are randomly chosen, convenient, represents population and heterogeneous

Multistage Sample

Sampling schemes that combine several sampling methods

Systematic Sample

Sample drawn by selecting individuals systematically from a sampling frame, when a relationship between the order of the sampling frame and variables of interest is absent, this can be a representative

Pilot

Small trial run of a survey to check whether questions are clear

Convenience Sampling

Consists of individuals readily available; fails to be a representative mostly