Question

What do I do when my Welch test and Mann-Whitney tests have conflicting p-values/ interpretations?

Independent Samples T-Test
		Test		Statistic		df		p
Lead_Measured_(mg/kg)		Student		-2.048		90.000		0.044
		Welch		-2.048		64.477		0.045
		Mann-Whitney		920.500				0.285

Table 3. A Student, Welch, and Mann-Whitney t-test.

This is what I have collected from my data, and I do not know how to properly interpret it.

My confidence level is 95% with and alpha value of 5%.

Answer 1

The p-values are conflicting because the Welch test is a parametric test and Mann-Whitney is a non-parametric test.

If the Lead_Measured variable is normally distributed then make the interpretation based on the Welch test, otherwise use the p-value of the Mann-Whitney test because the Welch test requires the assumption that the variable is normally distributed.

If the p-value is greater than 0.05 that means there is not a significant difference and when it is less than 0.05 that means there is a significant difference in the given problem.

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