In: Statistics and Probability
To determine if their 2.00 inch washers are properly adjusted, Duncan & Hall Inc. has decided to use an x‾-Chart which uses the range to estimate the variability in the sample.
Table:
| 
 Period  | 
 obs1  | 
 obs2  | 
 obs3  | 
 obs4  | 
 obs5  | 
 Sample Mean  | 
 Sample Range  | 
| 
 1  | 
 1.96  | 
 2.05  | 
 1.97  | 
 1.97  | 
 2  | 
 1.99  | 
 0.09  | 
| 
 2  | 
 2  | 
 2.05  | 
 1.95  | 
 2  | 
 2.05  | 
 2.01  | 
 0.1  | 
| 
 3  | 
 2.04  | 
 1.96  | 
 1.96  | 
 1.97  | 
 1.96  | 
 1.978  | 
 0.08  | 
| 
 4  | 
 1.97  | 
 2  | 
 1.98  | 
 1.99  | 
 1.99  | 
 1.986  | 
 0.03  | 
| 
 5  | 
 1.97  | 
 2.05  | 
 1.98  | 
 2.04  | 
 2.05  | 
 2.018  | 
 0.08  | 
| 
 6  | 
 2.03  | 
 2.05  | 
 2.01  | 
 1.96  | 
 1.96  | 
 2.002  | 
 0.09  | 
| 
 7  | 
 2.02  | 
 1.98  | 
 2.03  | 
 1.96  | 
 2.01  | 
 2  | 
 0.07  | 
| 
 8  | 
 1.99  | 
 1.99  | 
 2.01  | 
 1.98  | 
 1.97  | 
 1.988  | 
 0.04  | 
| 
 9  | 
 2  | 
 2.03  | 
 1.99  | 
 1.95  | 
 1.97  | 
 1.988  | 
 0.08  | 
| 
 10  | 
 1.95  | 
 1.99  | 
 1.98  | 
 1.96  | 
 2  | 
 1.976  | 
 0.05  | 
| 
 11  | 
 2.03  | 
 1.98  | 
 1.96  | 
 2.02  | 
 2.04  | 
 2.006  | 
 0.08  | 
Step 5 of 7:
Use the following sample data, taken from the next time period,
to determine if the process is "In Control" or "Out of
Control".
Observations: 2,1.98,1.93,1.95,1.96
Sample Mean: 1.964
| Period | obs1 | obs2 | obs3 | obs4 | obs5 | Sample Mean | Sample Range | 
| 1 | 1.96 | 2.05 | 1.97 | 1.97 | 2 | 1.99 | 0.09 | 
| 2 | 2 | 2.05 | 1.95 | 2 | 2.05 | 2.01 | 0.1 | 
| 3 | 2.04 | 1.96 | 1.96 | 1.97 | 1.96 | 1.978 | 0.08 | 
| 4 | 1.97 | 2 | 1.98 | 1.99 | 1.99 | 1.986 | 0.03 | 
| 5 | 1.97 | 2.05 | 1.98 | 2.04 | 2.05 | 2.018 | 0.08 | 
| 6 | 2.03 | 2.05 | 2.01 | 1.96 | 1.96 | 2.002 | 0.09 | 
| 7 | 2.02 | 1.98 | 2.03 | 1.96 | 2.01 | 2 | 0.07 | 
| 8 | 1.99 | 1.99 | 2.01 | 1.98 | 1.97 | 1.988 | 0.04 | 
| 9 | 2 | 2.03 | 1.99 | 1.95 | 1.97 | 1.988 | 0.08 | 
| 10 | 1.95 | 1.99 | 1.98 | 1.96 | 2 | 1.976 | 0.05 | 
| 11 | 2.03 | 1.98 | 1.96 | 2.02 | 2.04 | 2.006 | 0.08 | 
| total | 21.942 | 0.79 | |||||
| average | 1.995 | 0.072 | 
from above :
| sample mean x̅ = | 1.995 | ||||
| average range R̅ = | 0.072 | ||||
| sample size n = | 5 | ||||
| for sample size n=5, criitcal value of constant A2= | 0.577 | ||||
| control line (CL) = x̅= | 1.995 | ||||
| upper control limit =x̅+3*A2R̅ = | 2.037 | ||||
| lower control limit =x̅-3*A2R̅ = | 1.953 | ||||
as 1.964 falls between upper and lower control limit ; therefore process is "In Control"