Statistical Procedure

This procedure can be used when the:

Outcome (Dependent) variable is a Continuous and skewed / Ordinal measure
Exposure (Independent) variable is 2 independent groups

Present this graphically using a Box and Whisker Plot

In SPSS select: Graphs > Chart Builder - Gallery – Boxplot | Simple Boxplot

Analyse this in SPSS using:

Analyze >NonParametric Tests > Legacy Dialogs > 2 Independent Samples
Use the Exact button and select Exact, Statistics button and select Quartiles

The Exact Sig. (2-tailed) is the p-value.

Use Analyze > Descriptives Statistics > Explore to obtain Medians of each group. Select the Statistics button - Percentiles and limit the Display to Statistics.

Report this quoting the:

Median difference, 95% Confidence Intervals and p-value
Use Confidence Interval Analysis (CIA)Medians and their Differences | Unpaired Samples to calculate these values

References

Chapter 15, p 540 in Discovering Statistics using SPSS 3rd Edition, A. Field, Sage Publications (2009) (ISBN: 9781847879073)
Testing for Differences between groups in the Statistics for the Terrified package

Please Report any issues to Brian Yuen