Category Archives: Mann-Whitney U test

Choosing the right statistical test

I cheat.  Well, I use “cheat” sheets.  I’ve had plenty of statistics training, but honestly, my brain just doesn’t want to hold onto the assumptions associated with this or that test.  So I create little charts or tables, which I reference often.  This frees up brain space to continually re-assess the pros and cons of buying a used Jeep Wrangler versus a Subaru WRX (three years strong and I still haven’t decided).

Anyway…here’s a quick reference guide for choosing a statistical test:

Answer the following questions:

  1. What is my variable type?
  2. Is the comparison group data paired or unpaired? (i.e., can you link data from individual respondents in the two comparison groups or not)
  3. What is the sample size?

Once you’ve answered these questions, use the following to identify which statistical test of significance to use:

Variable type

Paired data

Sample size

(in each group)

Test of significance

Categorical

No

>5

Chi-square

<5

Fisher’s exact test

Yes

N/A

NcNemar’s Test

Continuous

No

>30

Independent samples t-test

<30

Mann-Whitney U test

Yes

>30

Paired t-test

<30

Wilcoxon signed-rank test

Ordinal

  No

N/A

Mann-Whitney U test

  Yes

N/A

Wilcoxon signed-rank test

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Filed under CME, Fisher's exact test, Mann-Whitney U test, McNemar's Test, Statistics, t-test, Wilcoxon signed rank test