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XRCHART Statement |
See SHWXR3 in the SAS/QC Sample Library |
By default,
the XRCHART statement estimates the process mean () and standard deviation (
)from the data, as in the previous example. However,
there are applications in which standard values
(
and
) are available
based, for instance, on previous experience or
extensive sampling. You can specify these values with the MU0=
and SIGMA0= options.
For example, suppose it is known that the adhesive coating
process introduced in the previous example has a mean of
1260 and standard deviation of 15. The following
statements specify these standard values:
title 'Specifying Standard Process Mean and Standard Deviation'; symbol v=dot c=salmon; proc shewhart history=tape; xrchart weight*sample / mu0 = 1260 sigma0 = 15 xsymbol = mu0 cframe = bigb cinfill = ywh cconnect = salmon; run;
The XSYMBOL= option specifies the label for the central line on
the chart.
The resulting
and R charts are shown in Output 43.2.1.
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You can also specify and
with the
variables _MEAN_ and _STDDEV_ in a LIMITS= data set,
as illustrated by the following statements:
data tapelim; length _var_ _subgrp_ _type_ $8; _var_ = 'weight'; _subgrp_ = 'sample'; _type_ = 'STANDARD'; _limitn_ = 5; _mean_ = 1260; _stddev_ = 15; proc shewhart history=tape limits=tapelim; xrchart weight*sample / xsymbol=mu0; run;
The variables _VAR_ and _SUBGRP_ are required, and their values must match the process and subgroup-variable, respectively, specified in the XRCHART statement. The bookkeeping variable _TYPE_ is not required, but it is recommended to indicate that the variables _MEAN_ and _STDDEV_ provide standard values rather than estimated values.
The resulting charts (not shown here) are identical to those shown in Output 43.2.1.
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