We follow [Review of Economic Studies 52 (1985) 1] approach to modify the s
tandard consumer demand theory so that socio-demographic variables can be f
ormally incorporated into the demand systems. Our modified theory not only
includes all previous approaches to this problem as special cases but also
allows the useful interpretations of household production and subsistence e
xpenditure. (C) 2001 Elsevier Science BY All rights reserved.