Household income, women’s income share and food calorie intake in South Western Nigeria
Introduction
A wide range of empirical literature has provided evidence that the level of per-capita calorie intake has a strong positive but non-linear relationship with household income, after controlling for household and demographic variables (Boius et al., 1992; Subramanian and Deaton, 1996; Grimard, 1996).1 Prior to 1987, calorie-income elasticity for low-income populations throughout the developing world was estimated to be between 0.4 and 0.8 (Boius and Haddad, 1992). Thus, income increases for the poor as a food policy strategy have received strong justification in that it is expected to reduce malnutrition (Alderman, 1986).
However, Behrman et al. (1987) analyzed ICRISAT data for India, and found calorie-income elasticity estimates that were not significantly different from zero. They concluded that the linkage between income and nutrient consumption is weak and that nutrient improvements should not be expected with income gains in low income communities. This result was reinforced by Boius et al. (1992) who estimated calorie intake-total expenditure elasticity ranging between 0.08 and 0.14 with four different estimation techniques using a sample of Philippine farm households. Boius and Haddad (1992), argue that several studies after Behrman et al. (1987) reported calorie-income elasticity estimates which are in most cases lower than 0.2.
This revisionist school attributed the previous high estimates of calorie-income elasticity to two major sources. The first source is the wide use of calories estimated from food expenditure data rather than direct collection of data on food intake quantities, due to the dearth of food quantity information in household surveys. The second source of upward bias is believed to be the endogeneity of household income in the calorie intake – income model.
The use of calorie intake quantities from food expenditure data creates two kinds of upward bias in the estimate of calorie-income elasticity. The first is non-classical measurement error bias2 and the second is aggregation bias.3 This study addresses these problems by using data collected directly on actual food intake quantities to estimate calorie-income elasticity.
Upward bias in calorie-income elasticity estimate which results from endogeneity of household income is also of two kinds namely: simultaneity bias4 and omitted variable bias.5 In this study, I adopt the instrumental variable technique (IV) to address this problem of endogeneity of income.
On the other hand, the conventional school of thought which support the traditional view that calorie-income elasticities are sizeable at least among low income households argue that recent low estimates of calorie-income elasticity in households could arise from two sources. First is the frequent use of current income as a measure of wealth rather than permanent income (Behrman and Deolalikar, 1990),6 while the second is measurement error in income and expenditure. A major problem associated with data collected in developing countries is the difficulty in obtaining accurate data on income and expenditure.7 Both the use of current income and measurement error in the data would bias the ordinary least square regression estimate of calorie-income elasticity downwards.8
Per-capita expenditure is therefore used in place of current income in this study since it is a better proxy for permanent income. Furthermore, the use of per capita expenditure as proxy for income reduces measurement error in income since it is easier to get information on expenditures than on income in developing countries. To further reduce the magnitude of error, I used income, expenditure and daily calorie intake values which are averages over 12 fortnightly visits to each sample household.
The second point of investigation in this study is the effect of women share of income on calorie intake in low income households. Studies that investigate the impact of changes in household resource control pattern on calorie intake are not common. No such study is available for Nigeria. Empirical investigation into the relationship between women income share and other outcome variables such as food expenditure share, fertility, child survival, young children’s weight for height, and household expenditure are more common (Thomas, 1990, Thomas, 1992, Thomas, 1993). Hoddinott and Haddad (1995), using data from Cote De ‘Ivoire found a positive but small marginal effect of women’s income share on household food budget share. A doubling of the proportion of household cash income received by wives would lead to a meagre 1.9% rise in budget share of food eaten within the household. Hopkins et al. (1994) found that in Niger that changes in female annual income, while controlling for male income impacted positively on household food expenditures. These results, they claim, hold for both earned and non-labor income. Thomas, 1990, Thomas, 1992, Thomas, 1993 found that in Brazil, the identity of the household member controlling income affects nutrient intake, fertility, child survival, and young children’s weight for height, and household expenditure.
On the whole, the observed impact of women’s income share on household expenditure patterns is generally agreed to be a reflection of gender differentiated preferences. However empirical literature on Africa concerning this issue is still very limited and is principally because of the dearth of disaggregated household data on income and consumption. The analysis in this paper in based on household consumption, income, and expenditure data disaggregated by gender and thus gives us a rare opportunity to examine the effect of changes in the pattern of resource control on per caput calorie intake. Not many studies have examined the effect of changes in women income share on the quantity of calorie intake by household members in Africa. Most of the previous studies that examined the influence of women income on food consumption estimated women income share elasticity for food expenditure or food expenditure shares, rather than calorie intake which is the focus in this paper.
This paper hopes to contribute to the growing literature on determinants of calorie intake at the household level by investigating the response of calorie intake of individuals in the household to increases in both per capita expenditure and the share of household income controlled by women. The model estimated in this paper also allows for differential income responses for individuals, taking account of the effect of age and sex.9
The major findings of this study are as follows. First, calorie-income elasticity is estimated by IV as 0.194 and this suggests that calorie intake does not get a substantial share of marginal increases in household income. Thus, increasing household disposable income may not be a very effective strategy for bringing about increased food energy intake among low income populations in Nigeria.
The instrumental variable (IV) estimate of calorie intake-women’s income share elasticity is −0.04. We show that this negative marginal response is neither a consequence of reallocation of income towards more expensive and low calorie food sources nor an evidence of positive transaction cost resulting from imperfect substitution between male and female income in food consumption. This estimate is a rejection of the hypothesis that per caput calorie intake is positively related to increasing women share of household income and suggests that wealth redistribution from men to women would not increase per caput food energy intake in low income households in rural south western Nigeria.
Furthermore, the estimate of calorie-income elasticity is about four times the size of the estimate of calorie intake-women’s income share elasticity. This suggests that female-income targeting may not be as effective in raising calorie intake levels of household members as male-income targeting.
In addition, the results show that the OLS estimates of per capita expenditure and women share of income coefficient are smaller than the 2SLS estimates of the same coefficient. This downward bias of OLS estimate of elasticity coefficient is an indication that classical measurement error bias may be a more important source of bias in this investigation than the other potential sources of bias discussed earlier.
Finally, it is observed that the OLS and 2SLS estimates of women share of income are both negative, showing some consistency in the sign attached to the coefficient of per capita expenditure and women’s income variables irrespective of type of estimator (i.e. OLS or 2SLS).
Section snippets
Importance of food calories intake
Economic analysis of calorie consumption by households derives from the important role calories play in the definition of important welfare concepts such as health and productivity.10 According to Maxwell and Frankenberger (1992), enough food is mostly defined with emphasis on calorie and on requirements for
Theoretical framework
The analysis in this paper is approached from the point of view of a cooperative bargaining household model. There are two general classes of household models namely: income pooling and bargaining models. The income pooling models assume that household demand (or expenditure share) is not affected by the identity of the individual that earns the income. The effective constraint on the household welfare function is the pooled household income. On the other hand, the bargaining model throws away
Data collection procedure
A combination of cluster and systematic random sampling procedure was used to select 40 households from each of 12 rural/semi-urban communities in 3 of the 6 states that make up south-western Nigeria.14 Thus, a total of 160 households per state and 480 households in all were selected. However, the analysis used information from only 472 households, amounting to 2573 individuals who are at least 2 years of age (See Table 1).
Empirical model
The major hypotheses to be tested by the empirical model specified here are that:
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Increases in household income would increase per-caput calorie intake in low income rural households in south western Nigeria.
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Increases in women’s income share conditional on total household income would increase per-caput calorie intake in rural south western Nigeria.
The structural form equation derived from the individual preference model adopted as framework for this study is represented as
Econometric estimation issues
Estimating Eq. (5.1) by the ordinary least square (OLS) regression procedure would imply an assumption that all the right hand side variables in the model are truly exogenous.
First stage regression results and over-identification test
From the results of the first stage regressions shown in Table 2,30 we observe that total value of farm business assets and women’s share of household farm asset value are significant and positive predictors of per
Conclusion
This study investigates how per caput calorie intake in low income households of south western Nigeria respond to changes in total household income and women’s share of household income. I utilize primary data collected with multiple visits over a period of 6 months from 2573 individuals in 480 randomly selected households. The study addresses three major questions. First, “does a change in women’s income share significantly affect per caput calorie intake?” If it does, then what is the
Acknowledgement
I thank the African Economic Research Consortium, Nairobi Kenya and the Rockefeller Foundation Grant for Postdoctoral Research on the Economics of the Family in Low Income countries, Yale University, for providing the financial support for this study. The study benefited from comments and suggestions by John Strauss, Germano Mwabu, Eric Thorbecke, David Sahn, T. Paul Schultz, Garth Frazer, Christopher Udry, Robert Evenson, participants at the bi-annual research workshops of the African Economic
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