You have multiple atomic welders. The welders were put into place over time as t

Question

You have multiple atomic welders. The welders were put into place over time as the operation has grown. They aren't all the same or even from the same equipment manufacturer. As a result joint strength varies significantly between the different welders. Because capital cost of replacing them would be prohibitive you are looking for other options for improvement. A supplier has approached you about switching from the filler material you currently use to theirs. The filler is a consumable so this is a possible approach. The supplier claims that the new filler will improve weld strength in your application.

a) What is the best test to use to validate this claim?

b) what is the null hypothesis and alternative hypothesis?

c) Beyond whatever test you use to test for strength improvement, what test would you want to run before you made the switch?

d) Is there anything that you might want to calculate before you start testing ? What is it?

Explanation / Answer

(a) The best test for this purpose is the z-test for single mean.

(b) The null and alternative are:

H0: The weld strength is same as before

Ha: The weld strength has improved.

(c) Before the z-test we would like to run bartlet's test for equivalence of variance, as the z-test is valid only when the variances are same.

(d) We would like to calulate the sample standard deviations before going any further.

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