# AP Stats Ch. 4

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Population

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## Tags and Description

### 45 Terms

1

Population

Entire group we want information about

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2

Census

collects data from every individual in the population

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3

Sample

subset of the population from which we collect data

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4

sample survey

a study that collects data from a sample to learn about the population from which the sample was selected

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5

Conveince Sample

Selecting people from the population that are easier to reach

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6

Bias

A study that is likely over or underestimate the true data

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7

voluntary response sample

Allows people to choose to be in the sample by responding to a general invitation

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8

random sampling

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

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9

simple random sample (SRS)

of size n consists of n individuals from the population chosen in such a way that every set of n individuals has an equal chance to be the sample actually selected

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10

sampling without replacement

an individual can only be selected once

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11

sampling with replacement

an individual from a population can be selected more than once

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12

Strata

Groups of individuals in a population that are similar in some way that might affect their responses.

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13

stratified random sampling

choosing an SRS from each strata combining the SRSs into one overall sample.

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14

cluster

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

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15

Systematic random sampling

randomly choose one person and survey them and every kth person after them

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Cluster sampling

randomly select a cluster and survey everyone in the clusters

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17

Undercoverage

occurs when some groups in the population are left out of the process of choosing the sample

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18

Nonresponse

occurs when an individual chosen for the sample can't be contacted or refuses to participate

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19

response bias

systematic pattern of inaccurate answers to a survey question

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20

observational study

observes individuals and measures variables but does not influence the response

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21

response variable

measures the outcome of a study

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22

explanatory variable

a variable that we think explains or causes changes in the response variable

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23

confounding

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

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24

Experiment

A research method in which an investigator manipulates one or more factors to observe an outcome

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25

placebo

a treatment that has no active ingredient, but is otherwise like other treatments

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treatment

a specific condition applied to the individuals in an experiment

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27

experimental unit

the object to which a treatment is randomly assigned

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subject

experimental unit that is a person

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29

factor

a variable that is manipulated and may cause a change in the response variable (usually used when talking about multiple variables)

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30

levels

the specific values that the experimenter chooses for a factor (ex. yes or no, or 10th grade, 11th grade, or 12th grade)

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Control group

used to provide a baseline for comparing the effects of other treatments

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placebo effect

some subjects will respond to any treatment, even if inactive

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double-blind

neither the subject nor person administering experiment knows what treatment the subject is getting.

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34

single-blind

An experiment in which either the subjects or those who interact with them and measure the response variable, but not both, know which treatment a subject received.

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random assignment

assigning participants to experimental and control conditions by chance, thus minimizing preexisting differences between those assigned to the different groups

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control (similar to control group)

keeping other variables constant

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replication

giving each treatment to enough experimental units so that a difference in the effects of the treatments can be distinguished from chance variation.

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38

4 principles of experimental design

1. Comparison

2. Random Assignment

3. Control

4. Replication

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39

Completely randomized design

units are assigned to treatments completely at random

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40

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

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Randomized block design

random assignment is carried out within each block

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42

Matched pairs design

experimental design that uses blocks of size of two

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43

sampling variability

The fact that different random samples of the same size from the same population produce different estimates

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statistically significant

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

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45

Experiment - causation Sample/survey - inference

what shows causation and what allows inferences

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