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•
A
variable
is a characteristic that differs from one individual observation to next.
•
Some, such as the color of a person’s eye, are
categorical
, and some, such as a family’s income, are
quantitative
.
Cornell’s Ranking is neither – it is an
ordinal
variable
•
We can organize these counts into a frequency table, which records the totals and the category names.
•
Frequency tables and relative frequency tables describe the distribution of a categorical variable because they name the possible categories and
tell how frequently each occurs.
•
In a contingency table, the distribution of a variable by itself is called its
marginal distribution
.
•
The distribution of a variable obtained by restricting the Who to consider only a smaller group of individuals is called a
conditional
distribution
.
•
Does the histogram have a single, central hump or several separated bumps?
•
Humps in a histogram are called modes.
•
A histogram with one main peak is dubbed unimodal; histograms with two peaks are bimodal; histograms with three or more peaks
are called multimodal.
•
Formula for the mean is
:
n
y
∑
=
=
ns
observatio
of
number
Total
the mean is the point at which a histogram of the data would balance.
Think of the mean like the point at which a seesaw is at balance
The range of the data is the difference between the maximum and minimum values
•
Quartiles divide the data into four equal sections. The lower quartile is the median of the half of the data below the median; the upper quartile is
the median of the half of the data above the median.
•
The difference between the quartiles is the IQR, so
IQR = upper quartile – lower quartile
•
Five number summary:
•
Minimum (min)
•
First quartile (Q
1
)
•
Median
•
Third Quartile (Q
3
)
•
Maximum
•
Box plot: Central box spans the IQR. Line in the box marks the median. Lines extend from the box to mark min and max.
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 Spring '08
 ABDUS,S.

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