Another factor credited with reducing fertility is the improvement in birth control
technology, which reduced the monetary and psychic cost of limiting births, and provided
techniques controlled by women, which were independent of sex. The major advances in
technology occurred in the 1960s with the introduction of oral steroids (the pill) and the intra-
uterine device (IUD), followed by further refinements in their delivery systems. Traditional
mechanisms for population control such as abortion, infanticide, coitus interruptus, and condoms
have nonetheless allowed individuals to adjust their family size and affect population growth in
various periods and parts of the world, well before the advent of these modern means of birth
control. Although they may have facilitated the later demographic transition, these birth control
technologies do not appear to have been necessary.
Microeconomic models of fertility behaviour
Willis (1973) adapted a comparative advantage trade model to the household lifetime fertility
choice problem, wherein women’s education was assumed to enhance women’s productivity only
in the market, and thereby increase the relative price of home production and decrease their
demand for fertility. In his economic treatise on the family, Becker (1981) assigns a central role
to market/non-market specialization of spouses in the household, with childbearing and rearing
being the dominant non-market production activity traditionally performed by women.
To place more structure on fertility choices, Becker (1960; 1981) and Willis (1973)
hypothesize that parents viewed the human capital of their children (child quality) as a substitute
for their number of children (child quantity). If this were the case, then by definition income-
compensated cross-price effects should be positive between child quantity and quality. In other
words, increasing the price of children, for example by reducing the cost of birth control, would
directly decrease fertility and indirectly increase the demand for child quality (with income held
constant). Conversely, increasing the wage returns to schooling in the labour market would
directly increase the demand for schooling and indirectly decrease the demand for births. Becker
and Lewis (1974) postulate further that the income elasticity of demand for child quality exceeded
the positive income elasticity for child quantity, which could account for the paradoxical decline
in fertility with growth in income, without having to assume that children (quantity) are an
‘inferior’ good for which income effects are negative, or to show increases in women’s value of
their time in the modern economy caused the decline in their fertility.