Various authors have proposed agreement indices for measuring nominal scale response agreement between two judges. Two situations may occur. Either the categories of the nominal scale are defined in advance and both raters use the same categories, or the categories are not defined in advance and the number of categories used by each rater is different. For the former case, the kappa statistic by Cohen (1960) is a popular measure. For the latter case, agreement measures have been proposed by Brennan and Light (1974), Hubert (1977), and Janson and Vegelius (1978, 1982). To choose the best or most appropriate coefficient, the various measures need to be better understood. The behavior of J and [gamma] in the general nominal case is a topic for further investigation. For the moment, only J exhibits none of the four undesirable properties described in this article and may for that reason be preferred over [gamma].