biased
any systematic failure of a sampling method to represent its population
strata
when groups of experimental units are similar, they are gathered into these groups
census
a sample that consists of the entire population
cluster
sampling design in which entire groups are chosen at random
completely randomized
type of experiment in which all experimental units have an equal chance of receiving any treatment
confounding
when the levels of one factor are associated with the levels of another factor so their effects cannot be separated
control
aspects of the experiment that we know may have an effect on the response, but that are not the factors being studied
control group
experimental units assigned to a baseline treatment level
convenience
sampling design where individuals are chosen based on who is easily available
double blind
neither the subjects nor the people who have contact with them know which treatment a subject has received
experimental units
individuals on which an experiment is done
experiments
study in which subjects are randomly assigned to treatments
factor
variable whose levels are controlled by the experimenter
heterogeneous
not similar in makeup
homogeneous
similar in makeup
level
specific values that the experimenter chooses a factor
matched pairs
type of study in which subjects who are similar in ways not under study may be grouped together and then compared with each other on the variables of interest
multistage
sampling schemes that combine several sampling methods
nonresponse
type of bias that is problematic because the intended sample is incomplete
observational study
study based on data in which no treatments have been assigned to subjects
outcome
an individual result of a component of a simulation
placebo
treatment known to have no effect, administered so that all groups experience the same conditions
placebo effect
the tendency of many human subjects to show a response even when administered a fake treatment
population
the entire group of individuals or instances about whom we hope to learn
prospective
observational study in which subjects are followed to observe future outcomes
random behavior
an occurrence for which we know what outcomes could happen, but not which particular values will happen
randomization
process by which each individual is given a fair chance of selection
response
type of bias that is problematic because false information may be given
retrospective
observational study in which subjects are selected and then their previous conditions or behaviors are determined
sample
a (representative) subset of a population, examined in hope of learning about a population
simple random
sampling design in which each set of n elements in the population has an equal chance of selection
sampling frame
a list of individuals from whom the sample is drawn
sampling variability
the natural tendency of randomly drawn samples to differ, one from another
sample survey
a study that asks questions of a sample drawn from some population in the hope of learning something about the entire population
simulation
models random events by using random numbers to specify outcomes with relative frequencies that correspond to the true real-world relative frequencies we are trying to model
single blind
when either the subjects or the people who have contact with them do not know which treatment a subject has received
statistically significant
when an observed difference is too large to believe that it is likely to have occurred naturally
block
a subdivision of the population
stratified
sampling design in which the population is divided into several strata, and random samples are then drawn from each stratum
subjects
people who are studied
systematic
sample drawn by select an individual from a list and then each of the next N individuals from the sampling frame
treatment
the process or intervention applied to randomly assigned experimental units
trial
the sequence of several components representing events that we are pretending will take place
undercoverage
type of bias that is problematic because some groups are not represented in the sample
voluntary response
type of bias that is problematic because those who volunteer tend to have strong negative opinions
voluntary response
sampling design where individuals can choose on their own whether to participate in the sample
wording bias
a type of response bias where the question is posed to achieve a desired result