Statistics
Summer 2007
Exam 2 Cheat Sheet
•
Observational Study
 Observes individuals and measures variables of interest but does not attempt to influence the responses; describes some group or
situation.
•
Experiment
 Deliberately imposes some treatment on individuals in order to observe their responses; purpose of an experiment is to study whether
treatment causes a change in response.
•
Confounded
 Two variables are confounded when their effects on a response variable cannot be distinguished from each other.
•
Population
 Entire group of individuals about which we want info.
•
Sample
 A part of a population from which we actually collect info; we use a sample to draw conclusions about entire populations.
•
Sample Design
 Describes exactly how to choose a sample from the population.
•
Biased
 If a design of a statistical study systematically favors certain outcomes.
•
Voluntary Response Sample
 People who choose themselves by responding to a broad appeal. They are biased.
•
Simple Random Sample (SRS)
 Of size
n
consists in such a way, every set has an equal chance to be selected.
•
Table of Random Digits
 A long stride of the digits 0, 1, 2, …, 7, 8, 9
o
Each entry is equally likely to be any of the 10 digits 09.
o
The entries are independent of each other.
•
Using Table B
:
o
Step 1
:
Label
: give each member of the population a numerical label of the same length.
o
Step 2
:
Table
: Read from Table B successive groups of digits of the length you used as labels.
•
Probability Sample
 Sample chosen by chance.
•
Stratified Random Sample
 First classify the population into groups of similar individuals called
Strata
. Then choose a separate SRS in each stratum
and combine these SRSs to form the full sample.
•
Undercoverage
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 Summer '07
 AllStats145
 Statistics, Null hypothesis, Statistical hypothesis testing

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