Statistical Procedure

This procedure can be used when the:

Outcome (Dependent) variable is a Continuous and Normally distributed 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 Box Plot

Analyse this in SPSS using:

Analyze >Compare Means > One-Way ANOVA
Use the Post Hoc button and select Bonferroni, Options button and select Descriptive Plot

Report this quoting the:

overall p-value and the differences, 95%CI between groups following Post Hoc comparisons
Use the confidence intervals output by SPSS

Comments

An alternative plot is Graphs > Chart Builder - Gallery - Bar | Simple Error bar

References

Chapter 10, p 347 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