[Roaming through methodology. VII. Reproducibility of measurements]

Reproducibility measurements are important for a proper interpretation of medical data. Kappa is the most adequate measure for categorical variables. Kappa adjusts the observed agreement for chance agreement. The interpretation of kappa is rather difficult. The kappa value is influenced by the number of categories used for classification and the prevalence of scores of the observers. For continuous variables the Pearson correlation coefficient can be used, keeping in mind its ignoring systematic errors and its dependence on the heterogeneity of the data. Another method to assess reproducibility for continuous variables is the method of limits of agreement. This method distinguishes systematic and random errors, and quantifies the differences in the dimension of the measurements. In general, the interpretation of the various measures of agreement is helped by a visual presentation of the data in a table or figure.