# AP Statistics Chapter 2

## 40 terms

### observational study

observe outcomes without imposing any treatment

### experiment

actively impose some treatment in order to observe the response

### experimental unit

the single individual to which the different treatments are assigned

### factor

the explanatory variable

### level

a specific value for the factor

what you measure

### treatment

a specific experimental condition applied to the units

### control group

a group that is used to compare the factor against; can be a placebo or old item

### placebo

a dummy treatment that can have no pysical effect

### blinding

method used so that units do not know which treatment they are getting

### double blind

neither the units nor the evaluator know which treatment a subject received

### control

principle of experimental design achieved by not allowing extraneous variables to affect the response by comparing treatment groups to a control group

### replication

principle of experimental design; doing the experiment multiple times on many subjects to quantify the natural variation in the experiment

### randomization

principle of experimental design; the use of chance to assign subjects to the treatments

### completely randomized

experimental design where all experimental units are allocated at random among all treatments

### randomized block

experimental design where units are blocked into homogenous groups and then randomly assigned to treatments

### matched pairs

experimental design where experimental units are matched according to similar characteristics and each unit of the pair is randomly assigned to a different treatment. if possible have each unit do both treatments in random order.

### dependent

the assignment of treatments in matched pairs design is

### confounding variable

the effect of the "___________" variable on the response cannot be separated from the effects of the explanatory variable

### completely randomized design

confounding does not occur in a ________

### ways to gather data

surveys, opinion polls, interviews, studies, experiments

### population

the entire group of individuals that we want information about

### census

a complete count of the population

### sample

a part of the population to examine in order to gather information

### generalize the population

samples result in/are used to ______

### sampling design

refers to he method used to choose the sample from the population

### sampling frame

a list of every individual in the population

### Simple Random Sample

individuals chosen where every individual or set of n individuals has an equal chance of being selected...name out of a hat

### Stratified Random Sample

population is divided into homgenous groups, and then SRS's are taken from the groups

### Systematic Random Sample

randomly select a starting point and select sample with a specified approach...3rd door, every 5th after

### cluster sample

based upon location; randomply pick a location and sample all there

### Multistage Sample

select succesively smaller groups within the population in stages, using SRS's at each stage

### random digit table

way to take an SRS using a series of numbers in columns and rows

### bias

a sytematic error in measuring the estimate; favors certain outcomes

### Voluntary Response Bias

people choose to respond; usually those with very strong opinions

### Convenience Sampling Bias

Bias that results from asking people who are easy to talk to... surveying outside mall doors

### Undercoverage Bias

bias because some of the groups are left out of the sampling process....phone book surveys

### Nonresponse bias

bias that occurs when an individual chosen for sample can't be contacted or refuses to cooperate.....subscribers and telemarketers

### Response Bias

bias that occurs when the behavior of the respondent or the interviewer causes bias in the sample....lies to a police officer

### wording of the question

connotated or technical word usage that affects answers given