Eng Mgt 385 Statistical Process Control Stephen A

Eng. Mgt. 385 Statistical Process Control Stephen A. Raper Chapter 3 Continued

Shewharts Bowl Experiment • Read, reread, and read again the detail of Shewharts Bowl Experiment • Demonstrates that the larger the sample taken from the universe, it is more likely that the average of the samples will be close to the process average • Averages of the samples themselves will form a frequency distribution

Shewharts Bowl Experiment • The average of such a frequency distribution of xbar values tends to be near “mu” , the average of the universe • The spread of the distribution of the xbar values depends on the spread of the universe but also on the sample size “n”.

Shewharts Bowl Experiment • The larger the value of n, the less the spread of the xbar values • The standard deviation of the distribution of xbar values will be divided by the square root of n • Even if the universe is nonnormal, statistical theory says that the expected frequency distribution of the xbar values also will be normal

Shewharts Bowl Experiment • Relationship between sbar—subgroup sample standard deviations, and the universe standard deviation: = sbar/c 4 • Relationship between rbar –grand range of samples and the universe standard deviation: = rbar/d 2

Program Completed University of Missouri-Rolla Copyright 2001 Curators of University of Missouri