Consider a plastic injection molding process for a part with a target critical w
ID: 3180185 • Letter: C
Question
Consider a plastic injection molding process for a part with a target critical width dimension of 100 and a historic standard deviation of 8. Periodically, clogs form in one of the feeder lines, causing the mean width to change, As a result, the operator periodically takes random samples of size four. A recent sample yielded a sample mean of 101.4. Conduct a hypothesis test to determine whether true mean width has increased. Use a significance level of 0.02 and the confidence interval approach for your test.
Explanation / Answer
Below are the null and alternate hypothesis,
H0: mu = 100
H1: mu > 100
Value of test statistics,
t = (101.4 - 100)/(8/sqrt(4)) = 0.35
degrees of freedom = 3
p-value = 0.3747
As p-value is greater than the significance level of 0.02, we fail to reject the null hypothesis.
Hence there is not enough evidence that the true mean has increased.