2022 Introduction to Statistics in Research Mitchell 2nd ed

I N T R O T O R E S E A R C H : D A T A V I S U A L I Z A T I O N & C O M M O N S T A T T E S T S

Compare legacy dialog approach to newer approach

SPSS has two ways to approach conducting an Mann-Whitney U test. You can use the legacy dialog approach or the newer (independent samples) approach. The newer approach gives you quite a few additional tables and depending on the boxes checked, you get a box plot, confidence interval and a direct approach of interpreting significance.

Legacy Dialog Approach

New approach – independent samples

Let’s review the difference between “exact” and “asymptotic” significance. Exact significance calculates a p-value using the true distribution. Asymptotic calculates a p-value using an approximation to the true distribution. If you have a smaller sample size, you should expect these two to be different and normally “exact” will be more conservative. As a rule of thumb, use “exact” if your sample size is equal to or less than 30. Now let’s get back to communicating the results.

Keep in mind that you could have a narrative or a table but not both.

MANN-WHITNEY U TEST SAMPLE WRITE-UP Training method A had sales of (Mdn = $1540, n=11) and were higher than those in training method B (Mdn = $1300, n=11) . A Mann-Whitney test indicated that this difference was statistically significant, U = 22.5, Z = -2.497, p =.011, with a larger effect size, r = -.5324, 95% CI [80, 510].

139