Neoclassical theory uses unitary model to explain economic rationality of consumer behaviour. Based on Brazilian data, this paper aims to test the validity of unitary model for singles and the validity of Browning and Chiappori’s collective model for couples. We estimate the QUAIDS model, which is based on a flexible preference structure that allows for quadratic Engel curves. The results indicate that the symmetry hypothesis is rejected for singles and supports the collective model for Brazilian couples.