As a rule of thumb, we considered a difference to be substantial if it was greater or equal to 5% and statistical significant at the 10% level. This allowed the establishment of a list of pertinent interaction terms to be included in the original statistical models. The selection of interaction terms was carried out separately for urban and rural households, and for sub-populations excluding either the self-employed or the non-self-employed workers. For example lack of wage data for the self-employed (proxied by consumption) that make half of the female labour force is a limiting factor.