Question

Your Quality Engineer has told you that she fixed a long term problem with a forming process and has reduced the variability in the process. In the next production run you sample 31 items from the old process and 26 items from the improved process. Your standard deviations are;

SD old = 2.55

SD new = 1.59

What is the value for the test statistic in this case?

Answer 1

Value of the test statistic =(Sample Mean difference – Hypothesized difference)/square root of ((square of standard deviation of old process/number of items of old process)+ (square of standard deviation of new process/number of items of new process)

Here, Hypothesized difference is zero and sample mean difference is also zero as both process has reduced variability in the process. Sample Mean difference would be zero.

So, value of the test statistic=0/ square root of ((square of standard deviation of old process/number of items of old process)+ (square of standard deviation of new process/number of items of new process)

Value of the test statistic=zero