Term | Definition |
population | a statistical study of the entire group of individuals |
census | collects data from every individual in the population |
sample | a subset of individuals in the population |
bias | consistently underestimate or consistently overestimate |
convenience sampling | chooses individuals easiest to reach |
voluntary response sample | consists of people who choose themselves by responding to an invitation |
simple random sample | x number of individuals chosen randomly from the population |
table of random digits | a random and independent string of digits |
stratified random sample | classifying the population into groups of similar individuals and then used to form an SRS |
cluster sample | classifying the population into groups of individuals that are located near each other and then used to form an SRS |
undercoverage bias | some members of a population cannot be chosen in a sample |
nonresponse bias | when an individual chosen for a sample cannot be contacted or refuses to participate |
wording of questions | influences the answers given to a sample survey |
response bias | a systematic pattern of incorrect responses in a sample survey |
observational survey | observes individuals and variables, does not attempt to influence responses |
experiment | deliberately imposes a treatment on individuals |
confounding | when two variables are associated and their effects on a response variable cannot be distinguished |
treatment | a specific condition applied to individuals in an experiment |
experimental units | smallest collection of individuals to which treatments are applied |
subject | when experiment units are humans |
comparison | a design with two or more treatments |
random assignment | use chance to assign experimental units to treatments |
control | keep other variables that might affect the response the same for all groups |
replication | use enough experimental units in each group so any differences can be distinguished from chance difference between the groups |
statistically significant | an observed effect so large that it would rarely occur by chance |
completely randomized design | treatments are assigned to all the experimental units completely by chance |
control group | receives an inactive treatment or existing baseline treatment |
placebo effect | response to a dummy treatment |
double-blind experiment | neither the subjects nor those who interact with them know which treatment a subject received |
block | a group of experimental units that are known before the experiment to be similar in some way that is expected to affect the response |
randomized block design | the random assignment of experimental units to treatments is carried out separately within each block |
matched pairs design | a randomized blocked experiment in which each block consists pairs of similar experimental units |