Note from the research unit “Food and nutrition research in the global South” (Nutripass)
Institut de Recherche pour le Développement (IRD) / Université de Montpellier / SupAgro Higher School of Education in Agricultural Science, Montpellier, France
Focus on the metrics
We thank the CFS and the HLPE for this e-consultation in preparation of the report on Nutrition and Food Systems. Considering the purpose of the report, the Project Team’s experts will have to face a very heterogeneous literature with different indicators, units of analysis, outcomes and levels of representativeness. Therefore we invite the Project Team’s experts to pay special attention to metrics and carefully consider their definitions, scope, strengths and weaknesses. To illustrate our point, we will take the example of the challenge of studying nutrition outcomes at different units of analysis: household and individual-level.
The pathway between household and individual-level is complex and may vary according to the region, composition of the household and food insecurity level. For example, in Northern Ghana where extended households are comprised of several nuclear family units, it was found that distribution of food was more favorable for children of the head of the extended household than for children of other family units (1). In South Asia, numerous studies found that male family members received more nutritious food than women (2). Due to this risk of asymmetric intrahousehold distribution of food, household-level dietary outcomes cannot adequately reflect nutritional status of household members and great caution should be taken when interpreting studies with household and/or individual-level data.
A first example relates to a publication by our group where we studied the relationship between the use of supermarkets in the Greater Tunis and diet quality as measured by the Diet Quality Index-International (3). We found an improved diet quality among regular supermarket users but, as only the diet quality of the person in charge of food shopping was assessed and linked to the household food supply, it would have been inappropriate to generalize our results to all household members.
Another example relates to the metrics of dietary diversity which are defined as the number of food items or food groups consumed by an individual or household in a given period. Indicators of dietary diversity were developed because simple measures of access to food or dietary quality were lacking. The indicators were validated (4-6) and WHO (6), FANTA (7) and FAO (8) published guidelines to help standardize these metrics. An indicator of women’s dietary diversity was validated recently (9). In the global debate on nutrition-sensitive agriculture, a growing literature addresses the complex linkages between agriculture and nutrition in rural areas of developing countries (10-16). These studies use metrics of dietary diversity at either household or individual level but some of them confuse these different levels (12,13). While both these levels of dietary diversity are assessed in a somewhat similar way, their significance differs notably. The household-level dietary diversity is a proxy indicator of household economic access to food whereas the individual-level dietary diversity is a proxy indicator of micronutrient adequacy of the diet (4-9). Because of potential asymmetric intrahousehold distribution of foods, the household-level dietary diversity cannot be used as an indicator of individual food consumption and even less as an indicator of the nutritional status of household members.
Once again, we invite the Project Team’s experts to be especially cautious when reviewing studies that address linkages between any element of food systems (e.g. supermarket use or agriculture) and nutrition. Appropriate use of the metrics should be rigorously evaluated, and separate analysis of the results and conclusions should be considered according to whether the household or the individual-level were studied. Moreover, beyond the question of the unit of analysis, the Project Team’s experts should consider issues of the type of dietary assessment method used, the relevance of the metrics chosen, and their comparability and standardization.
References
(1) Leroy JL, Razak AA, Habicht JP (2008) Only children of the head of household benefit from increased household food diversity in northern Ghana. J Nutr 138(11):2258-63.
(2) Haddad L, Pena C, Nishida C, Quisumbing A, Slack A (1996) Food security and nutrition implications of intrahousehold bias: a review of literature. FCND Discussion paper 19. Washington, DC: International Food Policy Research Institute.
(3) Tessier S, Traissac P, Maire B, Bricas N, Eymard-Duvernay S, El Ati J, Delpeuch F (2008) Regular users of supermarkets in Greater Tunis have a slightly improved diet quality. J Nutr 138(4):768-74.
(4) Hoddinott J, Yohannes Y (2002) Dietary Diversity as a Household Food Security Indicator: Technical Appendix. Washington, D.C.: FHI 360/Food and Nutrition Technical Assistance project.
(5) Arimond M, Wiesmann D, Becquey E, Carriquiry A, Daniels MC, et al. (2010) Simple food group diversity indicators predict micronutrient adequacy of women’s diets in 5 diverse, resource-poor settings. J Nutr 140(11): 2059S–2069S.
(6) WHO (2010). Indicators for assessing infant and young child feeding practices. Part 2: measurement. World Health Organization, Geneva.
(7) Swindale A, Bilinsky P (2006) Household Dietary Diversity Score (HDDS) for Measurement of Household Food Access: Indicator Guide (v.2). Washington, D.C.: FHI 360/Food and Nutrition Technical Assistance project.
(8) FAO (2011) Guidelines for Measuring Household and Individual Dietary Diversity (Food and Agriculture Organization of the United Nations, Rome).
(9) Martin-Prével Y, Allemand P, Wiesmann D, Arimond M, Ballard T, et al. (2015) Moving forward on choosing a standard operational indicator of women’s dietary diversity (Food and Agriculture Organization of the United Nations, Rome).
(10) Zezza A, Tasciotti L (2010) Urban agriculture, poverty, and food security: Empirical evidence from a sample of developing countries. Food Policy 35: 265–73.
(11) Jones AD, Shrinivas A, Bezner-Kerr R (2014) Farm production diversity is associated with greater household dietary diversity in Malawi: Findings from nationally representative data. Food Policy 46:1–12.
(12) Leonardo WJ, Florin MJ, van de Ven GWJ, Udo H, Giller KE (2015) Which smallholder farmers benefit most from biomass production for food and biofuel? The case of Gondola district, central Mozambique. Biomass and Bioenergy 83: 257-68.
(13) Sibhatu KT, Krishna VV, Qaim M (2015) Production diversity and dietary diversity in smallholder farm households. Proc Natl Acad Sci U S A 112(34):10657-62.
(14) Herforth A (2010). Promotion of traditional African vegetables in Kenya and Tanzania: A case study of an intervention representing emerging imperatives in global nutrition. PhD Thesis, Cornell University.
(15) Keding G, Msuya J, Maass B, Krawinkel M (2012) Relating dietary diversity and food variety scores to vegetable production and socio-economic status of women in rural Tanzania. Food Security 4(1): 129–40.
(16) Kumar N, Harris J, Rawat R (2015) If They Grow It, Will They Eat and Grow? Evidence from Zambia on Agricultural Diversity and Child Undernutrition, The Journal of Development Studies, 51:8, 1060-1077.
Eric Verger