sample
a subset of individuals in the population from which we collect data
statistic
a number that describes some characteristic of a sample
population
the entire group of individuals we want information about in a statistical study
parameter
a number that describes some characteristic of the population
categorical variable
a variable that assigns labels that place each individual into a particular group, called a category
experiment
a study in which researchers deliberately impose treatments on individuals to measure their responses
statistics
the science and art of collecting, analyzing, and drawing conclusions from data
individuals
an object described by a set of data. individuals may be people, animals, or things
variables
any characteristic of an individual. a variable can take different values for different individuals
quantitative variable
variable that takes number values that are quantities-counts or measurements
census
collects data from every individual in the population
observational study
a study that observes individuals and measures variables of interest but does not attempt to influence the response (no treatment)
simple random sample
sample of size n is chosen in such a way that every group of n individuals in the population has an equal chance of being selected as a sample
stratified random sample
selects a sample by choosing an SRS from each stratum and combining the SRS’s into one overall sample
cluster sample
selects a sample by randomly choosing clusters and including each member of the selected cluster
convenience sampling
selects individuals from a population who are easy to reach
voluntary response sampling
allows individuals to choose to be in the sample by responding to a general invitation. for example, an online survey
random sampling
involves using a random process to determine which members of a population are included in the sample
placebo
a treatment that has no active ingredient but is otherwise like other treatments
placebo effect
describes the fact that some subjects respond favorably to any treatment, even an inactive one (placebo).