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Example: Calculating the Mean and Standard
Deviation. Production supervisor May Kitt wants to determine how
long a certain process takes. She randomly picks six people, observes
them as they carry out the process, and records the number of min-
utes required:
15,5
9.25
10.0
125
120
85
Calculate the mean and standard deviation of the times.
Keys:
Display:
Description:
B(CLEAR] {Z}
Clears the statistical
registers.
15.5
n=1.0000
Enters the first time.
9.25
10
Enters the remaining
12.5
12
data.
8.5
n=6,0000
{z+5} {=}
%=11.2917
Calculates the mean.
{s} {sx}
sx=25808
Calculates the standard
deviation.
Calculating the Population Standard Deviation
The standard deviations calculated by {sx} and {s»} are the sam-
ple standard deviations. They assume that the data is a sampling of a
larger, complete set of data. If the data constitutes the entire popula-
tion of data, the true population standard deviation can be computed by
calculating the mean of the original data, adding the mean to the sta-
tistical data using [Z+], and then calculating the standard deviation.
64
5: Statistical Calculations
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