Page 60 - Intermediate Statistics for Dummies

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Chapter 2: Sorting through Statistical Techniques
Number of Putts
Total Score
83
30
83
31
83
33
84
26
The first step in looking for a connection between putts and total scores (or
any other quantitative variables) is to make what is called a scatterplot of the
data, which graphs your data set in two-dimensional space by using an x and
y plane. You can take a look at the scatterplot of the golf data in Figure 2-1.
Here, x represents the number of putts, and y represents the total score. For
example, the point in the lower-left corner of the graph represents someone
who had only 23 putts and a total score of 75. (For instructions on making a
scatterplot by using Minitab, see Chapter 4.) 39
Scatterplot of Total Score versus Number of Putts
120
Figure 2-1:
110
A scatter-
plot is
a two- Total Score 100
dimensional
graph you 90
can use to
look for
relation- 80
ships in
data. 20 25 30 35 40 45 50
Putts
According to Figure 2-1, it appears that as the number of putts increases, so
does total score. The relationship seems pretty strong — the number of putts
plays a big part in determining the total score.
Now you need a measure of how strong the relationship is between x and y
and whether it goes uphill or downhill. Correlation is the number that mea-
sures how close the points follow a straight line. Correlation is always
between –1.0 and +1.0, and the more closely the points follow a straight line,