Creating Box Charts from Raw Data
See SHWBOXA in the SAS/QC Sample Library
|
A petroleum company uses a turbine to heat water into
steam that is pumped into the ground to make
oil more viscous and easier to extract.
This process occurs 20 times daily, and
the amount of power (in kilowatts) used to
heat the water to the desired temperature is recorded.
The following statements create a SAS data set
that contains the power output measurements
for 20 days:
data turbine;
informat day date7.;
format day date5.;
label kwatts='Average Power Output';
input day @;
do i=1 to 10;
input kwatts @;
output;
end;
drop i;
datalines;
04JUL94 3196 3507 4050 3215 3583 3617 3789 3180 3505 3454
04JUL94 3417 3199 3613 3384 3475 3316 3556 3607 3364 3721
05JUL94 3390 3562 3413 3193 3635 3179 3348 3199 3413 3562
05JUL94 3428 3320 3745 3426 3849 3256 3841 3575 3752 3347
06JUL94 3478 3465 3445 3383 3684 3304 3398 3578 3348 3369
06JUL94 3670 3614 3307 3595 3448 3304 3385 3499 3781 3711
.
.
.
23JUL94 3421 3787 3454 3699 3307 3917 3292 3310 3283 3536
23JUL94 3756 3145 3571 3331 3725 3605 3547 3421 3257 3574
;
A listing of TURBINE is shown in Figure 32.1.
This data set is said to be in "strung-out" form since
each observation contains the day and power output
for a single heating.
The first 20 observations contain
the outputs for the first day, the second 20
observations contain the outputs for the second
day, and so on. Because the variable DAY classifies the
observations into rational subgroups, it is referred to
as the subgroup-variable. The variable KWATTS contains
the output measurements and is referred to as the
process variable (or process for short).
Kilowatt Power Output Data |
Obs |
day |
kwatts |
1 |
04JUL |
3196 |
2 |
04JUL |
3507 |
3 |
04JUL |
4050 |
4 |
04JUL |
3215 |
5 |
04JUL |
3583 |
6 |
04JUL |
3617 |
7 |
04JUL |
3789 |
8 |
04JUL |
3180 |
9 |
04JUL |
3505 |
10 |
04JUL |
3454 |
11 |
04JUL |
3417 |
12 |
04JUL |
3199 |
13 |
04JUL |
3613 |
14 |
04JUL |
3384 |
15 |
04JUL |
3475 |
16 |
04JUL |
3316 |
17 |
04JUL |
3556 |
18 |
04JUL |
3607 |
19 |
04JUL |
3364 |
20 |
04JUL |
3721 |
21 |
05JUL |
3390 |
22 |
05JUL |
3562 |
23 |
05JUL |
3413 |
24 |
05JUL |
3193 |
25 |
05JUL |
3635 |
26 |
05JUL |
3179 |
27 |
05JUL |
3348 |
28 |
05JUL |
3199 |
29 |
05JUL |
3413 |
30 |
05JUL |
3562 |
31 |
05JUL |
3428 |
32 |
05JUL |
3320 |
33 |
05JUL |
3745 |
34 |
05JUL |
3426 |
35 |
05JUL |
3849 |
36 |
05JUL |
3256 |
37 |
05JUL |
3841 |
38 |
05JUL |
3575 |
39 |
05JUL |
3752 |
40 |
05JUL |
3347 |
41 |
06JUL |
3478 |
42 |
06JUL |
3465 |
43 |
06JUL |
3445 |
44 |
06JUL |
3383 |
45 |
06JUL |
3684 |
46 |
06JUL |
3304 |
47 |
06JUL |
3398 |
48 |
06JUL |
3578 |
49 |
06JUL |
3348 |
50 |
06JUL |
3369 |
51 |
06JUL |
3670 |
52 |
06JUL |
3614 |
53 |
06JUL |
3307 |
54 |
06JUL |
3595 |
55 |
06JUL |
3448 |
56 |
06JUL |
3304 |
57 |
06JUL |
3385 |
58 |
06JUL |
3499 |
59 |
06JUL |
3781 |
60 |
06JUL |
3711 |
61 |
07JUL |
3448 |
62 |
07JUL |
3045 |
63 |
07JUL |
3446 |
64 |
07JUL |
3620 |
65 |
07JUL |
3466 |
66 |
07JUL |
3533 |
67 |
07JUL |
3590 |
68 |
07JUL |
3070 |
69 |
07JUL |
3499 |
70 |
07JUL |
3457 |
71 |
07JUL |
3411 |
72 |
07JUL |
3350 |
73 |
07JUL |
3417 |
74 |
07JUL |
3629 |
75 |
07JUL |
3400 |
76 |
07JUL |
3381 |
77 |
07JUL |
3309 |
78 |
07JUL |
3608 |
79 |
07JUL |
3438 |
80 |
07JUL |
3567 |
81 |
08JUL |
3568 |
82 |
08JUL |
2968 |
83 |
08JUL |
3514 |
84 |
08JUL |
3465 |
85 |
08JUL |
3175 |
86 |
08JUL |
3358 |
87 |
08JUL |
3460 |
88 |
08JUL |
3851 |
89 |
08JUL |
3845 |
90 |
08JUL |
2983 |
91 |
08JUL |
3410 |
92 |
08JUL |
3274 |
93 |
08JUL |
3590 |
94 |
08JUL |
3527 |
95 |
08JUL |
3509 |
96 |
08JUL |
3284 |
97 |
08JUL |
3457 |
98 |
08JUL |
3729 |
99 |
08JUL |
3916 |
100 |
08JUL |
3633 |
101 |
09JUL |
3153 |
102 |
09JUL |
3408 |
103 |
09JUL |
3741 |
104 |
09JUL |
3203 |
105 |
09JUL |
3047 |
106 |
09JUL |
3580 |
107 |
09JUL |
3571 |
108 |
09JUL |
3579 |
109 |
09JUL |
3602 |
110 |
09JUL |
3335 |
111 |
09JUL |
3494 |
112 |
09JUL |
3662 |
113 |
09JUL |
3586 |
114 |
09JUL |
3628 |
115 |
09JUL |
3881 |
116 |
09JUL |
3443 |
117 |
09JUL |
3456 |
118 |
09JUL |
3593 |
119 |
09JUL |
3827 |
120 |
09JUL |
3573 |
121 |
10JUL |
3594 |
122 |
10JUL |
3711 |
123 |
10JUL |
3369 |
124 |
10JUL |
3341 |
125 |
10JUL |
3611 |
126 |
10JUL |
3496 |
127 |
10JUL |
3554 |
128 |
10JUL |
3400 |
129 |
10JUL |
3295 |
130 |
10JUL |
3002 |
131 |
10JUL |
3495 |
132 |
10JUL |
3368 |
133 |
10JUL |
3726 |
134 |
10JUL |
3738 |
135 |
10JUL |
3250 |
136 |
10JUL |
3632 |
137 |
10JUL |
3415 |
138 |
10JUL |
3591 |
139 |
10JUL |
3787 |
140 |
10JUL |
3478 |
141 |
11JUL |
3482 |
142 |
11JUL |
3546 |
143 |
11JUL |
3196 |
144 |
11JUL |
3379 |
145 |
11JUL |
3559 |
146 |
11JUL |
3235 |
147 |
11JUL |
3549 |
148 |
11JUL |
3445 |
149 |
11JUL |
3413 |
150 |
11JUL |
3859 |
151 |
11JUL |
3330 |
152 |
11JUL |
3465 |
153 |
11JUL |
3994 |
154 |
11JUL |
3362 |
155 |
11JUL |
3309 |
156 |
11JUL |
3781 |
157 |
11JUL |
3211 |
158 |
11JUL |
3550 |
159 |
11JUL |
3637 |
160 |
11JUL |
3626 |
161 |
12JUL |
3152 |
162 |
12JUL |
3269 |
163 |
12JUL |
3431 |
164 |
12JUL |
3438 |
165 |
12JUL |
3575 |
166 |
12JUL |
3476 |
167 |
12JUL |
3115 |
168 |
12JUL |
3146 |
169 |
12JUL |
3731 |
170 |
12JUL |
3171 |
171 |
12JUL |
3206 |
172 |
12JUL |
3140 |
173 |
12JUL |
3562 |
174 |
12JUL |
3592 |
175 |
12JUL |
3722 |
176 |
12JUL |
3421 |
177 |
12JUL |
3471 |
178 |
12JUL |
3621 |
179 |
12JUL |
3361 |
180 |
12JUL |
3370 |
181 |
13JUL |
3421 |
182 |
13JUL |
3381 |
183 |
13JUL |
4040 |
184 |
13JUL |
3467 |
185 |
13JUL |
3475 |
186 |
13JUL |
3285 |
187 |
13JUL |
3619 |
188 |
13JUL |
3325 |
189 |
13JUL |
3317 |
190 |
13JUL |
3472 |
191 |
13JUL |
3296 |
192 |
13JUL |
3501 |
193 |
13JUL |
3366 |
194 |
13JUL |
3492 |
195 |
13JUL |
3367 |
196 |
13JUL |
3619 |
197 |
13JUL |
3550 |
198 |
13JUL |
3263 |
199 |
13JUL |
3355 |
200 |
13JUL |
3510 |
201 |
14JUL |
3795 |
202 |
14JUL |
3872 |
203 |
14JUL |
3559 |
204 |
14JUL |
3432 |
205 |
14JUL |
3322 |
206 |
14JUL |
3587 |
207 |
14JUL |
3336 |
208 |
14JUL |
3732 |
209 |
14JUL |
3451 |
210 |
14JUL |
3215 |
211 |
14JUL |
3594 |
212 |
14JUL |
3410 |
213 |
14JUL |
3335 |
214 |
14JUL |
3216 |
215 |
14JUL |
3336 |
216 |
14JUL |
3638 |
217 |
14JUL |
3419 |
218 |
14JUL |
3515 |
219 |
14JUL |
3399 |
220 |
14JUL |
3709 |
221 |
15JUL |
3850 |
222 |
15JUL |
3431 |
223 |
15JUL |
3460 |
224 |
15JUL |
3623 |
225 |
15JUL |
3516 |
226 |
15JUL |
3810 |
227 |
15JUL |
3671 |
228 |
15JUL |
3602 |
229 |
15JUL |
3480 |
230 |
15JUL |
3388 |
231 |
15JUL |
3365 |
232 |
15JUL |
3845 |
233 |
15JUL |
3520 |
234 |
15JUL |
3708 |
235 |
15JUL |
3202 |
236 |
15JUL |
3365 |
237 |
15JUL |
3731 |
238 |
15JUL |
3840 |
239 |
15JUL |
3182 |
240 |
15JUL |
3677 |
241 |
16JUL |
3711 |
242 |
16JUL |
3648 |
243 |
16JUL |
3212 |
244 |
16JUL |
3664 |
245 |
16JUL |
3281 |
246 |
16JUL |
3371 |
247 |
16JUL |
3416 |
248 |
16JUL |
3636 |
249 |
16JUL |
3701 |
250 |
16JUL |
3385 |
251 |
16JUL |
3769 |
252 |
16JUL |
3586 |
253 |
16JUL |
3540 |
254 |
16JUL |
3703 |
255 |
16JUL |
3320 |
256 |
16JUL |
3323 |
257 |
16JUL |
3480 |
258 |
16JUL |
3750 |
259 |
16JUL |
3490 |
260 |
16JUL |
3395 |
261 |
17JUL |
3596 |
262 |
17JUL |
3436 |
263 |
17JUL |
3757 |
264 |
17JUL |
3288 |
265 |
17JUL |
3417 |
266 |
17JUL |
3331 |
267 |
17JUL |
3475 |
268 |
17JUL |
3600 |
269 |
17JUL |
3690 |
270 |
17JUL |
3534 |
271 |
17JUL |
3306 |
272 |
17JUL |
3077 |
273 |
17JUL |
3357 |
274 |
17JUL |
3528 |
275 |
17JUL |
3530 |
276 |
17JUL |
3327 |
277 |
17JUL |
3113 |
278 |
17JUL |
3812 |
279 |
17JUL |
3711 |
280 |
17JUL |
3599 |
281 |
18JUL |
3428 |
282 |
18JUL |
3760 |
283 |
18JUL |
3641 |
284 |
18JUL |
3393 |
285 |
18JUL |
3182 |
286 |
18JUL |
3381 |
287 |
18JUL |
3425 |
288 |
18JUL |
3467 |
289 |
18JUL |
3451 |
290 |
18JUL |
3189 |
291 |
18JUL |
3588 |
292 |
18JUL |
3484 |
293 |
18JUL |
3759 |
294 |
18JUL |
3292 |
295 |
18JUL |
3063 |
296 |
18JUL |
3442 |
297 |
18JUL |
3712 |
298 |
18JUL |
3061 |
299 |
18JUL |
3815 |
300 |
18JUL |
3339 |
301 |
19JUL |
3746 |
302 |
19JUL |
3426 |
303 |
19JUL |
3320 |
304 |
19JUL |
3819 |
305 |
19JUL |
3584 |
306 |
19JUL |
3877 |
307 |
19JUL |
3779 |
308 |
19JUL |
3506 |
309 |
19JUL |
3787 |
310 |
19JUL |
3676 |
311 |
19JUL |
3727 |
312 |
19JUL |
3366 |
313 |
19JUL |
3288 |
314 |
19JUL |
3684 |
315 |
19JUL |
3500 |
316 |
19JUL |
3501 |
317 |
19JUL |
3427 |
318 |
19JUL |
3508 |
319 |
19JUL |
3392 |
320 |
19JUL |
3814 |
321 |
20JUL |
3676 |
322 |
20JUL |
3475 |
323 |
20JUL |
3595 |
324 |
20JUL |
3122 |
325 |
20JUL |
3429 |
326 |
20JUL |
3474 |
327 |
20JUL |
3125 |
328 |
20JUL |
3307 |
329 |
20JUL |
3467 |
330 |
20JUL |
3832 |
331 |
20JUL |
3383 |
332 |
20JUL |
3114 |
333 |
20JUL |
3431 |
334 |
20JUL |
3693 |
335 |
20JUL |
3363 |
336 |
20JUL |
3486 |
337 |
20JUL |
3928 |
338 |
20JUL |
3753 |
339 |
20JUL |
3552 |
340 |
20JUL |
3524 |
341 |
21JUL |
3349 |
342 |
21JUL |
3422 |
343 |
21JUL |
3674 |
344 |
21JUL |
3501 |
345 |
21JUL |
3639 |
346 |
21JUL |
3682 |
347 |
21JUL |
3354 |
348 |
21JUL |
3595 |
349 |
21JUL |
3407 |
350 |
21JUL |
3400 |
351 |
21JUL |
3401 |
352 |
21JUL |
3359 |
353 |
21JUL |
3167 |
354 |
21JUL |
3524 |
355 |
21JUL |
3561 |
356 |
21JUL |
3801 |
357 |
21JUL |
3496 |
358 |
21JUL |
3476 |
359 |
21JUL |
3480 |
360 |
21JUL |
3570 |
361 |
22JUL |
3618 |
362 |
22JUL |
3324 |
363 |
22JUL |
3475 |
364 |
22JUL |
3621 |
365 |
22JUL |
3376 |
366 |
22JUL |
3540 |
367 |
22JUL |
3585 |
368 |
22JUL |
3320 |
369 |
22JUL |
3256 |
370 |
22JUL |
3443 |
371 |
22JUL |
3415 |
372 |
22JUL |
3445 |
373 |
22JUL |
3561 |
374 |
22JUL |
3494 |
375 |
22JUL |
3140 |
376 |
22JUL |
3090 |
377 |
22JUL |
3561 |
378 |
22JUL |
3800 |
379 |
22JUL |
3056 |
380 |
22JUL |
3536 |
381 |
23JUL |
3421 |
382 |
23JUL |
3787 |
383 |
23JUL |
3454 |
384 |
23JUL |
3699 |
385 |
23JUL |
3307 |
386 |
23JUL |
3917 |
387 |
23JUL |
3292 |
388 |
23JUL |
3310 |
389 |
23JUL |
3283 |
390 |
23JUL |
3536 |
391 |
23JUL |
3756 |
392 |
23JUL |
3145 |
393 |
23JUL |
3571 |
394 |
23JUL |
3331 |
395 |
23JUL |
3725 |
396 |
23JUL |
3605 |
397 |
23JUL |
3547 |
398 |
23JUL |
3421 |
399 |
23JUL |
3257 |
400 |
23JUL |
3574 |
|
Figure 32.1: Listing of the Data Set TURBINE
You can use a box chart to examine the
distribution of power output for each day
and to determine whether the mean level of the heating process
is in control.
The following statements create the box chart
shown in Figure 32.2:
title 'Box Chart for Power Output';
symbol v=dot c=salmon;
proc shewhart data=turbine;
boxchart kwatts*day / cframe = vligb
cboxes = dagr
cboxfill = ywh
cinfill = ligr;
run;
This example illustrates the basic form of the BOXCHART
statement. After the keyword BOXCHART,
you specify the process
to analyze (in this case, KWATTS), followed by an asterisk and
the subgroup-variable (DAY).
Figure 32.2: Box Chart for Power Output Data
The input data set is specified with the DATA= option in the
PROC SHEWHART statement.
By default, the BOXCHART statement requests an chart
superimposed with
box-and-whisker plots for each subgroup.
Table 32.1 lists the summary statistics
represented by each
plot. For details on the computation
of percentiles, see "Percentile Definitions" .
Table 32.1: Summary Statistics Represented by Box-and-Whisker Plots
Subgroup Summary Statistic
|
Feature of Box-and-Whisker Plot
|
Maximum | Endpoint of upper whisker |
Third quartile (75 th percentile) | Upper edge of box |
Median (50 th percentile) | Line inside box |
Mean | Symbol marker (in this example, a dot) |
First quartile (25 th percentile) | Lower edge of box |
Minimum | Endpoint of lower whisker |
The within-subgroup variation in power output is stable, as indicated
in Figure 32.2 by the edges of the boxes and the endpoints of
the whiskers.
Since the subgroup means, indicated by the dots, lie within
the control limits, you can
conclude that the heating process
is in statistical control.
The skeletal style of the box-and-whisker plots
shown in Figure 32.2 is the default.
You can request different styles,
as illustrated in Example 32.2.
By default, the control limits shown are
limits estimated from the data;
the formulas for the
limits are given in Table 32.23
and Table 32.24.
You can also create box charts in which the control limits
apply to the subgroup medians.
For example, the following statements
create the chart shown in Figure 32.3:
title 'Box Chart for Power Output';
symbol v=dot c=salmon;
proc shewhart data=turbine;
boxchart kwatts*day / controlstat = median
cframe = vligb
cboxes = dagr
cboxfill = ywh
cinfill = ligr;
run;
The CONTROLSTAT=MEDIAN option requests control limits
that apply to the medians.
Alternatively, you can specify the NOLIMITS option
to suppress the display of control limits and create
ordinary side-by-side box-and-whisker plots.
See Example 32.2.
Options such as CONTROLSTAT= and NOLIMITS are specified
after the slash (/) in the BOXCHART statement.
A complete list of options is
presented in the "Syntax" section.
Figure 32.3: Box Chart for Power Output Data
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.