How to do the test:

  1. State your Null Hypothesis glossary item: Null Hypothesis in the form:
    "There is no difference between the populations from which two unrelated samples come"
  2. Choose a Critical Significance Level (α: alpha) glossary item: Critical Significance Level
    This is typically α = 0.05
  3. Calculate the statistic
    Use a spreadsheet to calculate your results, or
    Access a helpsheet for SPSS
    and check here for data entry into SPSS
  4. Reject or accept your Null Hypothesisglossary item: Null Hypothesis
    Either compare the calculated statistic with Critical Value, glossary item: Critical Value
    NOTE: The calculation yields two values of the U statistic. Either can be used, but both the spreadsheet and SPSS use the smaller value. Thus:
    If U ≤ Ucritical → reject H0 → significant result
    If U > Ucritical → accept H0 → non-significant result
    Look at the calculated probability (P value) glossary item: probability
    If P ≤ α → reject H0 → significant result
    If P > α → accept H0 → non-significant result
  5. Report your results
    Plot your data using the appropriate graphs
    (Mann-Whitney U test: U = …, n1 = …, n2 = …, P = …)
    View an example report