AP STATS CHAPTER 4

Population

Population

The entire group of individuals about which we want information about

Census

Contacting EVERY memeber of the population to gather information

Sample

• Method of collecting information from the sample

• The part of the population from which we actually collect information. We use this infomation to draw conclusions on the entire population.

Bias

If it is statically favors certain outcomes

Convenient Sampling

Choosing individuals who are easiest to reach

Voluntary Response

Call-in (radio/news station), write-ins, internet polls

Nonresponse

When an individual in the sample refuses to anser or can’t be contatcted

Judgement

Researcher chooses sample based off who they feel represent popultion

Undercoverage

If people left out have different views than those sampled

Response bias

Wording of question

Simple Random Sample (SRS)

Everyone has an equal chance of people part of the sample

Stratified Random Sample

Classify the population into strata. Choose a seperate SRS in each stratum and combine these SRSs to form a full sample

Strata

Groups within the population of similiar individuals. Remember we want the stratas to be very different from one another and the individuals WITHIN the strata to be very similiar

Cluster Sample

Put population into clusters, randomly select a cluster, this is your sample

Cluster

Groups that mirror the characteristics of the population. Remember we want the clusters to be very different from one another and the individuals WITHIN the cluster to be very similiar

Explanatory Variable

Helps explain or influence changes in a response variable

Response Variable

Measures an outcome of a study

Lurking Variables

A variable that is not among the explanatory or response variables in a study by may influence the response variable

Retrospective Study

Looking at past data and making assumptions (observational study)

Prospective Study

A study that follows a group of individuals over a period of time

Experiment

A statistical study in which we actually do soemthing (treatment) to people, animals, or objects (experimental units) to observe the response

Random Assignment

The experimental units are assigned to treatments at random

Replication

Use enough experimental units in each group so that any differences in the effects of the treatments can be distinguished from chance differences between the groups

Completely Randomized Design

Experiment desgined in a way that the treatments are assigned to all the experimental untis completely by chance (random assignment)

Placebo

Sham treatment desgined to create blinding

Double blind

Neither the subjects nor those who interact with them and measure the response variable know which treatment a subject received, reduces bias

Statistically Significant

An observed effect so large that it would rarely occur by chance

Block

A group of experimental units that are known before the experiment to be similiar in some way that is expected to affect the response of the treatments, reduces variation

Randomized Block Design

The random assignment of experimental units to treatments is carried out seperately within each block.

Matched Pairs Design

A type of randomized block desgin that creates the block by pairing up similiar experimental units

Confounding Variables

Variables not controlled for that affect results