User-written Stata program: agrm

In the context of his research on perceptual agreement, Cees van der Eijk (2001, Quality & Quantity: 35, 325–341) indicates that empirical measures that resort to the standard deviation of the response distribution capture not only consensus but also skewedness. Thus they are inappropriate measures of agreement. His alternative measure of agreement, A, circumvents this problem and yields unbiased figures for all kinds of ordered rating scales. It first decomposes the frequency distribution into constituent layers, that is, row vectors for which consensus can be unambiguously defined. It then computes the weighted average degree of agreement. Given the lack of a corresponding ado-file, the user-written agrm command allows you to directly calculate van der Eijk’s index of agreement, A, in Stata. Aside from a broad range of basic programming features such as low-level parsing and specifying additional program options, argm also entails more advanced techniques such as handling empty categories and handling numerical missing values. Moreover, it highlights the potential of nested loops and local macros in the context of multiple permutations. Finally, the agrm command is especially suited for showing how Stata’s matrix language, Mata, provides a powerful environment for handling vectors and matrices.