chapter 11 vocab

population

the entire group of people or objects about which information is desired

sample

a (typically small) part of the population selected to be representative of the population

sample survey

surveys designed to ask questions of a small group of people in the hope of learning something about the entire population

biased

when a sampling method systematically over-represents certain segments of the population and systematically under-represents others

randomization

selecting samples at random to prevent bias

census

a study that examines data on the entire population

parameter

a numerical characteristic of the population

statistic

a numerical characteristic of the sample

simple random sample (SRS)

individuals are selected so that all possible combinations of individuals are equally likely to be in the sample

sampling frame

list of individuals that the sample is picked from

sampling variability

sample-to-sample differences

homogeneous groups

consists of members sharing similar or identical traits

heterogeneous groups

groups that are diverse/different

strata

groups of similar individuals

stratified random sample

divide the population into groups of similar individuals called strata; choose an SRS in each stratum to form the full sample

cluster sampling

involves the division of a population into smaller groups, called clusters. Ideally, there is heterogeneity within each cluster, and clusters are similar to one another in their composition. A simple random sample of clusters is selected from the population to form the sample of clusters. Data are collected from all observations in the selected clusters

multistage sampling

Sampling schemes that combine several methods are called multistage samples (not on exam)

systematic sampling

the first individual is chosen at random; then a system or rule is used to choose all other individuals

respondents

people answering/participating in the surveys

voluntary response sample

people choose themselves to be in the sample by responding to a general appeal

convenience sampling

individuals who are easiest to reach are chosen for the sample

undercoverage

some groups are left out of the process of choosing the sample

nonresponse bias

an individual chosen for the sample cannot be contacted or refuses to cooperate. Note, the sample must be chosen first

response bias

anything in the survey design that influences the responses. The behavior of the individual or the interviewer may also influence the accuracy of the response. Self-reported responses fall under this category as well

sample size

refers to the number of observational units contained in the sample

sample design

the method we use to select the sample

unbiased

if the values of the statistic from different samples are centered at that parameter value

voluntary response bias

caused by the corresponding sample