Normal Quantile Plot

The workbooks and a pdf-version of this user manual can be downloaded from here.

Normal Quantile plots (or Q-Q-plots) are also used to assess the normality of data (Wang & Bushman, 1998). The expectation is that all data points are approximately on a straight line, which would indicate that the dispersion of the data follows a standard normal distribution.

This part in Meta-Essentials (see Figure 25) consists of four sections: a table with studies, a plot, regression estimates, and an input option for the calculation of sample quantiles. The table presents the study names, the estimated normal quantile and the sample quantile. The plot gives these normal and sample quantiles as well as a regression line through them.

With the input option, the user can choose to base the sample quantiles on either ‘Standardized residuals’ or ‘Z-scores’ (see red rectangle in Figure 25).

Figure 25: Example of Normal Quantile Plot part of the Publication Bias Analysis sheet

References

Wang, M. C., & Bushman, B. J. (1998). Using the normal quantile plot to explore meta-analytic data sets. Psychological Methods, 3(1), 46-54. dx.doi.org/10.1037/1082-989x.3.1.46