AP Statistics Chapter 4

population

the entire group of individuals we want information about

census

collects data from every individual in the population

sample

a subset of individuals in the population from which we actually collect data

sample survey

a study that uses an organized plan to choose a sample that represents some specific population

convenience sample

choosing individuals who are easiest to reach

bias

using a method that favors some outcomes over others; if a statistical study consistently under or overestimates the value you want to know

voluntary response sample

consists of people who choose to be in the sample by responding to a general invitation

random sampling

using a chance process to determine which members of a population are included in the sample

simple random sample (SRS)

chosen in such a way that every group of n individuals in the population has an equal chance to be selected as the sample

stratified random sample

a sampling design in which the population is classified into strata

strata

group of similar individuals

cluster sample

a sampling design in which the population is classified into clusters

cluster

group of individuals that are located near each other

sampling errors

lead to bias

undercoverage

occurs when some members of the population cannot be chosen in a sample

nonresponse

occurs when an individual chosen for the sample cannot be contacted or refuses to participate

response bias

anything in a survey design that influences responses (can be gender, race, ethnicity, behavior, etc)

wording of questions

confusing or leading questions can introduce strong bias

inference

inferring information about a population from what we know about a sample

observational study

observes individuals and measures variables of interest but does not attempt to influence the responses

experiment

deliberately imposes some treatment on individuals to measure their responses

confounding

occurs when two variables are associated in such a way that their effects on a response variable cannot be distinguished from each other

treatment

a specific condition applied to the individuals in an experiment

experimental units

the smallest collection of individuals to which treatments are applied

subjects

when the experimental units are human beings

random assignment

assigning the experimental units to treatments using a chance process

completely randomized design

the experimental units are assigned to the treatments completely by chance

control

keeping other variables that might affect the response the same for all groups

double-blind

neither the subjects nor those who interact with them and measure the response variable know which treatment a subject received

placebo effect

the response to a dummy treatment

statistically significant

an observed so large that it would rarely occur by chance

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 to the treatments

randomized block design

the random assignment of experimental units to treatments is carried out separately within each block

informed consent

an ethical principle that research participants be told enough to enable them to choose whether they wish to participate

confidentiality

an ethical principle that all data about the research participants is protected

matched pairs design

a type of randomized block design, the idea is to create blocks by matching pairs of similar experimental units

lack of realism

can prevent us from generalizing results from an experiment