What is a variable?
characteristic that can vary in value among subjects - measurable
What is the measurement scale?
the values the variable can take
What are the two main types of variables?
quantitative and categorical (qualitative)
What are nominal variables?
categorical variable that is unordered, has a quality not a magnitude
What are interval variables?
quantitative variables that have levels of scale/magnitude with defined distances
What are ordinal variables?
variables that have a natural order, but no defined distance. levels have a greater than or less than magnitude
What is a discrete variable?
variable with possible values that form a set of separate numbers, finite number of possible values
What is a continuous variable?
variable that can take an infinite continuum of possible real number values (can’t list all the possible values)
What is randomization?
a method for achieving good sample representation
What is a (simple) random sample?
each possible sample has the same chance of being selected
What is a sampling frame?
List of all subjects in the population
What are some ways to collect data?
sample survey, experiment, observational study
What is sampling error?
how much the statistic differs from the parameter that it predicts
What are 3 types of bias?
sampling, response and non-response
What is sampling bias?
using nonprobablity sampling (volunteer sampling), having undercoverage
What is response bias?
incorrect responses, misleading or confusing questions, question wording, interview leading
What is non-response bias?
sampled subjects can’t be reached or refuse to participate, fail to answer some questions
What is systematic random sampling?
selecting samples using a skip number (N/n = k), selects every kth subject
What is stratified random sampling?
divides the population into separate groups (strata) and then selects a simple random sample from each stratum (can be proportional or disproportional to population)
What is cluster sampling?
divides the population into a large number of clusters and selects a simple random sample from each cluster, use the subjects in those clusters for the sample
What is the difference between stratified and cluster sampling?
a stratified sample uses every stratum, a cluster sample uses a sample of the clusters (not all of them)
What is multistage sampling?
uses a combination of sampling methods