Quality Digest, March 5, 2018

Figure 13:  X-chart for the 100 Wire Length Data

While Figure 2 had no points outside the three-standard-deviation limits, Figure 14 has 11

out of 200 points (5.5%) outside the three-sigma limits.  The data are not homogeneous, so we

conclude that the underlying process was operated unpredictably.

---

Donald J. Wheeler

The Empirical Rule

www.spcpress.com/pdf/DJW328.pdf

9

March 2018

25

20

15

10

5

19.3

12.9

6.4

Figure 14:  X-chart for the 200 Bead Board Data

While Figure 3 had 3 points outside the three-standard-deviation limits, Figure 15 has 57 out

of 259 points (22%) outside the three -sigma limits.  The data are not homogeneous, so we

conclude that the underlying process was operated unpredictably.

700

800

900

1000

1100

1200

X

1005.7

937.0

868.3