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[
Statistics
]:
A collection of procedures and principles for gathering data and analyzing information in order to help people make decisions when faced with uncertainty.
.
[
Variable
]:
a characteristic which changes when from observation to observation in a population.
[
Categorical (Qualitative) Variable
]:
A variable whose values cannot be interpreted as numbers.
With categorical data, we can replace numbers with letters, symbols, etc.
Note:
When analyzing categorical data, we will typically work with
counts
or
percentages
of objects.
[
Numerical (Quantitative) Variable
]:
Measurements or counts, values which have meanings as numbers.
Discrete
:
If the set of all possible values, when pictured on the number line, consists only of isolated points. The most common type of discrete variable we will encounter is a
counting variable
.
Continuous
: If the set of all values, when pictured on the number line, consists of intervals.
[
Census
]: Look at every object or individual in the population.
We know everything exactly, but it takes a lot of time and money, may even be impossible to do if measurements are
destructive (e.g., average lightbulb lifetime).
[
Sampling Variability
]:
The differences between samples from the same population
[
Random Sample
]:
A subset of the population selected so that every individual has a specified probability of being part of the sample.
[
Simple Random Sample
]:
A random subset of size
n
from a population where the subset is chosen in such a way that every possible subset of size
n
has the same chance of being
selected as any other.
[
Sample Survey
]:
A method of gathering opinions and information from each individual included in the sample.
Possible problems:
nonresponse bias
and
volunteer sample
, both cause a nonrepresentative sample
[
CaseControl Study
]:
A study in which ‘cases’ having a particular condition are compared to ‘controls’ who do not.
The idea is to compare them to see how they differ on the
variable of interest.
[
Experiment
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 Spring '08
 dongling
 Statistics

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