[R-meta] Meta-analysis of single group attitude scores

[Tommy van Steen]

Dear all,

I have a question about my meta-analytic approach in a project that I’m working on.
In this project, we are conducting a meta-analysis of attitudes. The study outcome variable is the mean attitude score on a scale (often a Likert-scale type survey or single item).

I am trying to figure out what the best way is to conduct a meta-analysis based on this type of data as the data comes from single groups and studies vary in the number of answering possibilities on the Likert-scales.

My thought would be to transform the study mean into a z-score by subtracting the neutral score (e.g. ‘3' in a 5-point scale study) from the study mean and divide the outcome by the standard deviation of the study mean. This way, the z-score reflects whether the attitude was positive (f the z-score is positive) or negative (if the z-score is negative), with 0 being neutral. I would then use this z-score as the effect size for my meta-analysis.

Based on this, I have three questions:
1. Is this a sensible option? 
2. If so, how should I calculate the study weights? (As z-scores typically have an SD of 1 if I understand correctly.)
3. How would I run the meta-analysis based on these z-scores? (Simply loading the scores as effect sizes in an SMD meta-analysis using the metafor-package seems odd perhaps?)

Thank you very much for your time and thoughts.

With kind regards,
Tommy van Steen