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Weighted Mean and Grouped Standard Deviation
The followi^g procedure
calculates
the weighted mean and
grouped
standard
deviation. The weighted mean is the mean of data points
x1,
xz, ...rn
occurring
with
weights
wt,
wz,
...TJ)n
The weights can be non-
integer or integer
values (frequencies).
Grouped standard deviation is
the
standard
deviation
of
data
points
x"L,
xz, ...rn occurring at non-negative
integer
frequencies
fr,
fz,
...f".
To
calculate
weighted
mean
andf
or
grouped standard
deviation:
L
Enter
the
data
into two STAI hsts-one for the
numbers and
one
for
the weights or
frequencies.
The number and
its
weight
(frequency) must have the same item number
in
each
list.
Give
bottr lists meaningful names. (You do not need to name the cur-
rent list,
but
naming
it
avoids possible confusion
later.)
2.
From
the STAI
menu, press
ffi,
then
ffi.
3.Pressffi.DesignatethelistcontainingthenumberSasthe
r-variable
by
pressing
the appropriate menu k*y.
(If
the
current
list is
unnamed, pressing
ffi
selects
it.)
4.
Designate
the
list
containing the weights or frequencies
as
the y-
variable
by
pressing
the
appropriate menu
k*y.
Ignore the
message
indicating the current
model.
5.
Press
ffi.
6.Tocalcu1atetheweightedmean,PreSsffi.Tocalcu1atethe
grouped standard deviation,
Press
.
Exampler Weighted
tlean
and Standard DeYiation
of
Grouped
Data.
Your manufacturing company purchases
a
certain
part four
times a year. Last year's
purchases
were:
Pricef
Part
$4.25
Number
250
of
Parts
$4.60 $4.70
$4.10
800 900
1000
4: Statistics
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