AP Stat Chapter 4

Population

Entire group of individuals that are of interest in a study

Census

collects data from every individual in the population

Sample

subset of individuals in the population

Convenience sampling bias

a sample selected based on ease of access rather than random selection

Bias

makes the results of the study likely to over/underestimate

Voluntary response bias

allows people to 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 a sample

Simple random sample

chosen in such a way that every group of n individuals has an equal chance of being selected

Strata

individuals in a population who share characteristics thought to be associated with variables being measured in a study

Cluster

group of individuals in the population that are located near each other

Stratified random sampling

selects a sample by choosing an SRS from each stratum and combining them into one overall sample

Cluster sampling

randomly choosing clusters and including every member of the cluster in the study

Multistage sampling

sampling technique that uses a two-stage (or more) process to select a sample from a large population

systematic random sampling

selects a sample from an ordered arrangment

undercoverage

occurs when some member of the population are less likely or unable to be chosen

nonresponse bias

individuals chosen for the sample refuse to participate

Response bias

when there is a systematic pattern of inaccurate answers to a survey question

Observational study

examines data for a sample of individuals without attempting to influence the response (ex. survey)

Confounding

when the effects of an explanatory variable on a response variable cannot be distinguished from external factors

Experiment

deliberately imposes some treatment on individuals to measure their response

placebo

treatment with no active ingredient

treatment

condition applied to individuals in an experiment

factor

variable that is manipulated an may cause a change in the response

control group

a baseline for comparing the effect of the other treatments

Experimental design must have

Comparison, random assignment, control, and replication

Completely randomized design

experimental units are assigned to the treatments completely by chance

Block

a group of experimental units that are known before the experiment to be similar in some way that affects response

Block (or matched pairs) design

places experimental units into blocks before random assignment to reduce the variability of the response across experiments

Sampling variability

refers to the fact that different random samples of the population can produce different results

Sample size

larger samples tend to produce estimates closer to the true population value than smaller samples

Statistically significant

difference in observed results of a study is large enough that it cannot be explained by chance

scope of inference

the conclusions you can make from a study, specifically whether they apply to a larger population or establish a cause-and-effect relationship

Scope of experiments on non-humans

can be generalized to the population and establish causation

Scope of experiments on humans

cannot be generalized to the population but establish causation

Scope of good observational studies

can be generalized to the population but dont necessarily establish causation

Scope of bad observational studies

cant be generalized to the population nor establish causation

Establishing causation requires

strong association, consistent association across studies, large values of the explanatory are associated with strong responses, cause precede effect, and plausability

Placebo effect

describes the fact that some subjects in an experiment will respond favorably to an inactive treatment

Single-blind study

either the subject or experimenter doesn’t know who is receiving treatment

Double-blind

both the subject and the experimenter doesn’t knwo who is receiving treatment