Review
I
variable: any characteristic that is observed for the subject in
a study
I
categorical variable: each observation belongs to one of a
set of categories
I
quantitative: observations take numerical values that
represent different magnitudes of the variable
I
discrete variable: a quantitative variable is discrete if its
possible values form a set of separate number, such as
0,1,2,. . .
I
continuous variable: a quantitative variable is continuous if
its possible values form an interval
I
frequency table
I
mode: the category with the highest frequency
I
Dot Plots
I
Stem-and-Leaf Plots
The article ‘‘Effects of Aggregates and Microfillers
on the Flexural Properties of Concrete’’ reported
on a study of strength properties of high performance
concrete obtained by using superplasticizers and certain
binders. The accompanying data on flexural strength (in
MPa) appeared in the article cited:
5.9 7.2 7.3 6.3 8.1
6.8
7.0
7.6
6.8
6.5 7.0 6.3 7.9 9.0
8.2
8.7
7.8
9.7
7.4 7.7 9.7 7.8 7.7 11.6 11.3 11.8 10.7
stem
5
6
7
8
9
10
11
|
|
|
|
|
|
|
|
leaves (leaf unit: .1)
9
33588
00234677889
127
077
7
368
I
Histograms: a graph that uses bars to portray the
frequencies or the relative frequencies of the possible
outcomes for a quantitative variable
Construct a Histogram:
1. Divide the range of the data into intervals of equal width. For
a discrete variable with few values, use the actual possible
values.
2. Count the number of observations (the frequency) on each
interval, forming a frequency table.
3. On the horizontal axis, label the values or the endpoints of the
intervals. Draw a bar over each value or interval with height
equal to its frequency (or percentage), values of which are
marked on the vertical axis.
I
Unimodal
I
Bimodal
I
Outliers