See SHWBOXA in the SAS/QC Sample LibraryYou can save the control limits for a box chart in a SAS data set; this enables you to apply the control limits to future data (see Reading Preestablished Control Limits) or modify the limits with a DATA step program.
The following statements read measurements from the data set Turbine
(see Creating Box Charts from Raw Data) and save the control limits displayed in Figure 17.4 in a data set named TURBLIM:
proc shewhart data=Turbine; boxchart KWatts*Day / outlimits=Turblim nochart; run;
The OUTLIMITS= option names the data set containing the control limits, and the NOCHART option suppresses the display of the
chart. The data set Turblim
is listed in Figure 17.10.
Figure 17.10: The Data Set Turblim
Containing Control Limit Information
Control Limits for Power Output Data |
_VAR_ | _SUBGRP_ | _TYPE_ | _LIMITN_ | _ALPHA_ | _SIGMAS_ | _LCLX_ | _MEAN_ | _UCLX_ | _LCLS_ | _S_ | _UCLS_ | _STDDEV_ |
---|---|---|---|---|---|---|---|---|---|---|---|---|
KWatts | Day | ESTIMATE | 20 | .002699796 | 3 | 3351.92 | 3485.41 | 3618.90 | 100.207 | 196.396 | 292.584 | 198.996 |
The data set Turblim
contains one observation with the limits for process KWatts
. The variables _LCLX_
and _UCLX_
contain the lower and upper control limits for the means, and the variable _MEAN_
contains the central line. The value of _MEAN_
is an estimate of the process mean, and the value of _STDDEV_
is an estimate of the process standard deviation . The value of _LIMITN_
is the nominal sample size associated with the control limits, and the value of _SIGMAS_
is the multiple of associated with the control limits. The variables _VAR_
and _SUBGRP_
are bookkeeping variables that save the process and subgroup-variable. The variable _TYPE_
is a bookkeeping variable that indicates whether the values of _MEAN_
and _STDDEV_
are estimates or standard values.
The variables _LCLS_
, _S_
, and _UCLS_
are not used to create box charts, but they are included so that the data set Turblim
can be used to create an s chart; see XSCHART Statement: SHEWHART Procedure. If you specify the RANGES option in the BOXCHART statement, the variables _LCLR_
, _R_
, and _UCLR_
, rather than the variables _LCLS_
, _S_
, and _UCLS_
, are included in the OUTLIMITS= data set. These variables can be used to create an R chart; see XRCHART Statement: SHEWHART Procedure.
If you specify CONTROLSTAT=MEDIAN to request control limits for medians, the variables _LCLM_
and _UCLM_
, rather than the variables _LCLX_
and _UCLX_
, are included in the OUTLIMITS= data set as demonstrated by the following statements:
proc shewhart data=Turbine; boxchart KWatts*Day / outlimits = Turblim2 controlstat = median nochart; run;
Turblim2
is listed in Figure 17.11. For more information, see OUTLIMITS= Data Set.
Figure 17.11: The Data Set Turblim2
Containing Control Limit Information
Control Limits for Power Output Data |
_VAR_ | _SUBGRP_ | _TYPE_ | _LIMITN_ | _ALPHA_ | _SIGMAS_ | _LCLM_ | _MEAN_ | _UCLM_ | _LCLS_ | _S_ | _UCLS_ | _STDDEV_ |
---|---|---|---|---|---|---|---|---|---|---|---|---|
KWatts | Day | ESTIMATE | 20 | .002776264 | 3 | 3319.85 | 3481.63 | 3643.40 | 100.207 | 196.396 | 292.584 | 198.996 |
You can create an output data set containing both control limits and summary statistics with the OUTTABLE= option, as illustrated by the following statements:
title 'Summary Statistics and Control Limit Information'; proc shewhart data=Turbine; boxchart KWatts*Day / outtable=Turbtab nochart; run;
The data set Turbtab
is partially listed in Figure 17.12.
Figure 17.12: The OUTTABLE= Data Set Turbtab
Summary Statistics and Control Limit Information |
_VAR_ | Day | _SIGMAS_ | _LIMITN_ | _SUBN_ | _LCLX_ | _SUBX_ | _MEAN_ | _UCLX_ | _STDDEV_ | _EXLIM_ | _SUBMIN_ | _SUBQ1_ | _SUBMED_ | _SUBQ3_ | _SUBMAX_ |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
KWatts | 04JUL | 3 | 20 | 20 | 3351.92 | 3487.40 | 3485.41 | 3618.90 | 198.996 | 3180 | 3340.0 | 3490.0 | 3610.0 | 4050 | |
KWatts | 05JUL | 3 | 20 | 20 | 3351.92 | 3471.65 | 3485.41 | 3618.90 | 198.996 | 3179 | 3333.5 | 3419.5 | 3605.0 | 3849 | |
KWatts | 06JUL | 3 | 20 | 20 | 3351.92 | 3488.30 | 3485.41 | 3618.90 | 198.996 | 3304 | 3376.0 | 3456.5 | 3604.5 | 3781 | |
KWatts | 07JUL | 3 | 20 | 20 | 3351.92 | 3434.20 | 3485.41 | 3618.90 | 198.996 | 3045 | 3390.5 | 3447.0 | 3550.0 | 3629 | |
KWatts | 08JUL | 3 | 20 | 20 | 3351.92 | 3475.80 | 3485.41 | 3618.90 | 198.996 | 2968 | 3321.0 | 3487.0 | 3611.5 | 3916 | |
KWatts | 09JUL | 3 | 20 | 20 | 3351.92 | 3518.10 | 3485.41 | 3618.90 | 198.996 | 3047 | 3425.5 | 3576.0 | 3615.0 | 3881 | |
KWatts | 10JUL | 3 | 20 | 20 | 3351.92 | 3492.65 | 3485.41 | 3618.90 | 198.996 | 3002 | 3368.5 | 3495.5 | 3621.5 | 3787 | |
KWatts | 11JUL | 3 | 20 | 20 | 3351.92 | 3496.40 | 3485.41 | 3618.90 | 198.996 | 3196 | 3346.0 | 3473.5 | 3592.5 | 3994 | |
KWatts | 12JUL | 3 | 20 | 20 | 3351.92 | 3398.50 | 3485.41 | 3618.90 | 198.996 | 3115 | 3188.5 | 3426.0 | 3568.5 | 3731 | |
KWatts | 13JUL | 3 | 20 | 20 | 3351.92 | 3456.05 | 3485.41 | 3618.90 | 198.996 | 3263 | 3340.0 | 3444.0 | 3505.5 | 4040 | |
KWatts | 14JUL | 3 | 20 | 20 | 3351.92 | 3493.60 | 3485.41 | 3618.90 | 198.996 | 3215 | 3336.0 | 3441.5 | 3616.0 | 3872 | |
KWatts | 15JUL | 3 | 20 | 20 | 3351.92 | 3563.30 | 3485.41 | 3618.90 | 198.996 | 3182 | 3409.5 | 3561.0 | 3719.5 | 3850 | |
KWatts | 16JUL | 3 | 20 | 20 | 3351.92 | 3519.05 | 3485.41 | 3618.90 | 198.996 | 3212 | 3378.0 | 3515.0 | 3682.5 | 3769 | |
KWatts | 17JUL | 3 | 20 | 20 | 3351.92 | 3474.20 | 3485.41 | 3618.90 | 198.996 | 3077 | 3329.0 | 3501.5 | 3599.5 | 3812 | |
KWatts | 18JUL | 3 | 20 | 20 | 3351.92 | 3443.60 | 3485.41 | 3618.90 | 198.996 | 3061 | 3315.5 | 3435.0 | 3614.5 | 3815 | |
KWatts | 19JUL | 3 | 20 | 20 | 3351.92 | 3586.35 | 3485.41 | 3618.90 | 198.996 | 3288 | 3426.5 | 3546.0 | 3762.5 | 3877 | |
KWatts | 20JUL | 3 | 20 | 20 | 3351.92 | 3486.45 | 3485.41 | 3618.90 | 198.996 | 3114 | 3373.0 | 3474.5 | 3635.5 | 3928 | |
KWatts | 21JUL | 3 | 20 | 20 | 3351.92 | 3492.90 | 3485.41 | 3618.90 | 198.996 | 3167 | 3400.5 | 3488.0 | 3582.5 | 3801 | |
KWatts | 22JUL | 3 | 20 | 20 | 3351.92 | 3432.80 | 3485.41 | 3618.90 | 198.996 | 3056 | 3322.0 | 3460.0 | 3561.0 | 3800 | |
KWatts | 23JUL | 3 | 20 | 20 | 3351.92 | 3496.90 | 3485.41 | 3618.90 | 198.996 | 3145 | 3308.5 | 3495.0 | 3652.0 | 3917 |
This data set contains one observation for each subgroup sample. The variable _SUBMIN_
contains the subgroup minimums, and the variable _SUBQ1_
contains the first quartile for each subgroup. The variable _SUBX_
contains the subgroup means, and the variable _SUBMED_
contains the subgroup medians. The variable _SUBQ3_
contains the third quartiles, and the variable _SUBMAX_
contains the subgroup maximums. The variable _SUBN_
contains the subgroup sample sizes. The variables _LCLX_
and _UCLX_
contain the lower and upper control limits for the means. The variable _MEAN_
contains the central line. The variables _VAR_
and Day
contain the process name and values of the subgroup-variable, respectively. For more information, see OUTTABLE= Data Set.
An OUTTABLE= data set can be read later as a TABLE= data set. For example, the following statements read Turbtab
and display a box chart (not shown here) identical to the chart in Figure 17.4:
title 'Box Chart for Power Output'; proc shewhart table=Turbtab; boxchart KWatts*Day; label _SUBX_ = 'Average Power Output'; run;
Because the SHEWHART procedure simply displays the information in a TABLE= data set, you can use TABLE= data sets to create specialized control charts (see Specialized Control Charts: SHEWHART Procedure).
For more information, see TABLE= Data Set.