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TI-83 Worksheet Number 27
Statistics – Normal Probability Plot
Given the following set of data, check to see if it is close to a normal distribution.
Speed 29 34 34 28 30 29 38 31 29 34 32
31
31 27 37 29 26 24 34 36 31 34 36
To check for normality, we make a probability plot. This is constructed by first finding the
Z-scores for each of the numbers in the data list (recall the z-score = (data pointmean)/(standard deviation). We then plot the actual data on one axis and the
corresponding z-scores on the other axis. If the result is a perfect straight line, then the
data list is a linear transformation of the standard normal distribution and therefore the data
list is normal. The data list is close to normal of the plot is close to a straight line.
Key Strokes
Stat Enter
29 Enter 34 Enter … 36 Enter
2nd Statplot Enter Enter
▼ ► ► ► ► ► Enter
▼ 2nd L1
▼ ► Enter
Zoom 9
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Comment
Brings up List Editor. Select L1
Enter the data in L1
Selects and turns Plot1
Highlights the probability plot icon, the last
icon in the second row.
Enters L1 as the Data List
Selects the y-axis
as the Data Axis
(It does not make
any difference
which axis is the
data axis, but
convention
usually uses the y-axis as the data axis.)
Display the plot.
The solid
vertical line is at
the z-score =0
and will intersect
the mean of the
data. In this case
the line is fairly close to a straight line, so the
distribution of the data would be considered
close to normal.
WS 27 Page 1 of 1