In: Operations Management
You are considering relaxing your control requirements that determine what is acceptable quality; you have been using a 99.0% confidence interval but want to begin using a 97.5% confidence interval.
Your team has collected the following data from 4 samples of 7 observations each. The calculated standard deviation is 13.981.
Sample 1 | Sample 2 | Sample 3 | Sample 4 | |
Obs 1 | 392.2 | 415.1 | 413.6 | 399.7 |
Obs 2 | 392.3 | 408.1 | 394.9 | 402.3 |
Obs 3 | 405.4 | 428.6 | 410.1 | 400.6 |
Obs 4 | 410.3 | 398.2 | 410.8 | 427.6 |
Obs 5 | 423.3 | 403.3 | 423.2 | 385.8 |
Obs 6 | 413.9 | 421.1 | 402.7 | 431.0 |
Obs 7 | 426.7 | 433.5 | 385.8 | 405.9 |
What is the UCL for the mean given the new confidence interval of 97.5%? (Keep one decimal point in your answer)
Following table highlights average values of each sample consisting of 4 samples.
Average value of each sample = Sum of 7 observations / 7
Sample 1 |
Sample 2 |
Sample 3 |
Sample 4 |
|
Observation 1 |
392.2 |
415.1 |
413.6 |
399.7 |
Observation 2 |
392.3 |
408.1 |
394.9 |
402.3 |
Observation 3 |
405.4 |
428.6 |
410.1 |
400.6 |
Observation 4 |
410.3 |
398.2 |
410.8 |
427.6 |
Observation 5 |
423.3 |
403.3 |
423.2 |
385.8 |
Observation 6 |
413.9 |
421.1 |
402.7 |
431 |
Observation 7 |
426.7 |
433.5 |
385.8 |
405.9 |
Average = |
409.1571 |
415.4143 |
405.8714 |
407.5571 |
Thus , Xbar = Average of averages = ( 409.1571 + 415.4143 + 405.8714 + 407.5571) /4 = 409.5
Z value for 97.5% confidence interval = NORMSINV ( 0.9875 ) = 2.2414
Given are following data :
Standard deviation = 13.981
Sample size = n = 7 ( since there are 7 observations against each sample )
UCL for the mean given the 97.55 confidence interval
= Xbar + Z x Standard deviation / Square root ( sample size )
= 409.5 + 2.2414 x 13.981 / Square root ( 7 )
= 409.5 + 2.2414 x 13.981 /2.645
= 409.5 + 11.84
= 421.34
UCL FOR MEAN = 421.3 |