The greater the value of the index, the greater is the level of inequality. The properties of subgroup decomposability of Theil and other general entropy indices are well documented (e.g. Shorrocks, 1984, Cowell, 2005). In this case, some of the correlation captured here would not be explained by pre-marital household formation choices but rather by an increased norm for couple households to choose to work in similar occupations and industries, within similar wage groups. This caveat indicates that marital sorting may explain only part of the changes in intra-household labour supply behaviour.