View Full Version : Non zero P value for T test
12-14-2006, 02:33 PM
Here is a basic question. A person I know has a dataset with two columns. When they do a normality test for each column, it passes. One they do a hypothesis test for a two sample t-test in Minitab, the data shows a p-value of 0.229. Other t tests they ran on columns shows the P value = 0. What could be the cause of this? Do I need to run other tests, to find out the root cause? Which test? F-Test? Would that help? Any other test?
12-14-2006, 03:22 PM
Make sure the data is meeting the t-test assumptions (more than just normality):
12-15-2006, 07:25 AM
Thanks for the response. Let me share a bit on the approach of this person. They are measuring different length pins in manufacturing. Instead of putting all the pin sizes into one bundle, and doing a Hypothesis test (T-test) on the collective pin sizes, before and after the manufacturing change, they are doing a Hypothesis test (T-test) for each pin. The only problem is that one pin size doesnít show an improvement, but all the rest do. So I feel you need to look at things collectively. Suppose that someone was measuring a flavor ingredient change on M & Ms, but believed that each color would have a different variation, so did a Hypothesis test (T-test) on each color. Letís suppose that Green didnít show an improvement, but the other colors did. Now suppose that marketing pressure dictated putting the green in the mix, even thought it didnít show improvement. If there are an equal number of reds, greens, blues, yellows, etc., then the probability, by which it affected the outcome, would probably be a percentage that the green occupied, in relationship to the other colors, in the bag of M &Ms. I would appreciate any input on this approach.
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