Willingness to pay for small-quantity lipid-based nutrient supplements for women and children: Evidence from Ghana and Malawi

Small-quantity lipid-based nutrient supplements (SQ-LNS) are designed to enrich maternal and child diets with the objective of preventing undernutrition during the first 1,000 days. Scaling up the delivery of supplements such as SQ-LNS hinges on understanding private demand and creatively leveraging policy-relevant factors that might influence demand. We used longitudinal stated willingness-to-pay (WTP) data from contingent valuation studies that were integrated into randomized controlled nutrition trials in Ghana and Malawi to estimate private valuation of SQ-LNS during pregnancy, postpartum, and early childhood. We found that average stated WTP for a day’s supply of SQ-LNS was more than twice as high in Ghana than Malawi, indicating that demand for SQ-LNS (and by extension, the options for effective delivery of SQ-LNS) may be very context specific. We also examined factors associated with WTP, including intervention group, household socioeconomic status, birth outcomes, child growth, and maternal and child morbidity. In both sites, WTP was consistently negatively associated with household food insecurity, indicating that subsidization might be needed to permit food insecure households to acquire SQ-LNS if it is made available for purchase. In Ghana, WTP was higher among heads of household than among mothers, which may be related to control over household resources. Personal experience using SQ-LNS was not associated with WTP in either site. The DYAD‐G trial took place in a busy commercial corridor stretching through the Lower Manya Krobo and Yilo Krobo districts in the Eastern Region of Ghana, approximately 70 km north of Accra, the nation’s capital. Women were recruited for participation in the trial from the four main health facilities operating in the semi‐urban catchment area. On average, women who participated in the trial were approximately 27 years of age, had just over 7.5 years of formal education, and lived in food secure households (Adu‐Afarwuah et al., 2015). Recruitment for the DYAD‐M trial took place in the Mangochi district of the Southern Region of Malawi at a public hospital in the town of Mangochi, one rural hospital, and two rural health centres. Participants in the trial in Malawi were slightly younger than in Ghana (26.5 years of age on average) and had less formal schooling (average of approximately 4 years), and over a third lived in food insecure households (Ashorn, Alho, Ashorn, Cheung, Dewey, Harjunmaa, et al., 2015). In terms of the nutritional status of children under age five, in the Eastern Region of Ghana in 2014, 17% of children under age five were stunted, and 3.2% were wasted (Ghana Statistical Service, Ghana Health Service, & ICF International, 2015). In the Southern Region of Malawi, the rate of stunting among children under five was 41.8% in 2014, and 3.9% were wasted (National Statistical Office of Malawi, 2015). At both sites, women who were less than 20 weeks of gestation at a routine visit to one of the health facilities described above were recruited for participation in the trial. Recruitment was rolling, spanning the end of 2009 to the end of 2011 in Ghana and early 2011 to mid‐2012 in Malawi. A total sample of 1,320 women in Ghana and 1,391 women in Malawi were enrolled and randomized into one of three equally sized intervention groups (the randomized trials are detailed in Adu‐Afarwuah et al., 2015 and Ashorn, Alho, Ashorn, Cheung, Dewey, Harjunmaa, et al., 2015). Women randomized to the control group received a daily iron–folic acid capsule throughout pregnancy, a component of the standard of antenatal care in Ghana and Malawi. This group also received a placebo (low‐dose calcium) capsule during the first 6 months postpartum. Women in a second group received a daily multiple micronutrient capsule throughout pregnancy and during the first 6 months postpartum. Women in the third arm received SQ‐LNS for pregnant and lactating women (SQ‐LNS‐P&L) through pregnancy and during the first 6 months postpartum, and their infants received SQ‐LNS for child consumption (SQ‐LNS‐Child) from 6 to 18 months of age. Infants of women in the capsule groups did not receive any supplementation. Table A1 of the Supporting Information shows the nutrient content of the capsules and SQ‐LNS products. Ethical approval of the iLiNS Ghana study protocol (registered at http://clinicaltrials.gov as {“type”:”clinical-trial”,”attrs”:{“text”:”NCT00970866″,”term_id”:”NCT00970866″}}NCT00970866) was obtained from the ethics committees of the University of California, Davis, the Ghana Health Service, and the University of Ghana Noguchi Memorial Institute for Medical Research. Ethical approval of the iLiNS Malawi study protocol (registered at http://clinicaltrials.gov as {“type”:”clinical-trial”,”attrs”:{“text”:”NCT01239693″,”term_id”:”NCT01239693″}}NCT01239693) was obtained from the Research and Ethics Committee of the University of Malawi College of Medicine and by the Ethics Committee of Pirkanmaa Hospital District, Finland. Stated WTP data were collected from a random subsample (approximately 60% in Ghana and 45% in Malawi) of all households with women enrolled in the trial. Within a household, the WTP survey respondent was randomly assigned as either the mother participating in the trial or the head of her household, although in Malawi interviewing heads of household proved difficult, resulting in a substitution of the mother as the representative household respondent in almost all cases (approximately 94% of respondents). WTP data were collected five times, divided into three periods for the purposes of this analysis. Shortly after the beginning of maternal supplementation, we elicited WTP for SQ‐LNS‐P&L for maternal consumption during pregnancy. At around the 35th week of gestation, we again elicited WTP for SQ‐LNS‐P&L during pregnancy. These two time points comprise the pregnancy period. Approximately 3 months after the birth of the infant, we elicited WTP for SQ‐LNS‐P&L for maternal consumption during the first 6 months postpartum, and this time point represents the postpartum period. Finally, at approximately 6 and 18 months after the birth of the infant, we elicited WTP for SQ‐LNS‐Child for child consumption. A timeline of WTP data collection is available in the Supporting Information. Stated WTP for SQ‐LNS was elicited using a contingent valuation survey, described in detail in the Supporting Information. In short, after receiving brief information about undernutrition and nutrient supplements in general, respondents were asked to imagine SQ‐LNS were available for sale at a nearby kiosk and, bearing in mind their budget and regular expenses, were then led through a bidding tree to determine their maximum WTP. In Ghana, respondents were asked their WTP for a day’s supply (one 20‐g sachet), and in Malawi, respondents were asked their WTP for a week’s supply (seven 20 g sachets). For purposes of cross‐site comparison, WTP for a week’s supply in Malawi was converted to a daily rate for all analyses. The starting bids, which were randomized across respondents, were set at GH¢ 0.20, GH¢ 0.50, or GH¢ 1.00 (approximately US $0.13, $0.33, or $0.66) for a day’s supply in Ghana, and in Malawi, they were K100, K200, or K300 (approximately US $0.30, $0.60, or $0.90) for a week’s supply. The starting bids were chosen to be comparable to the prices consumers would face when purchasing traditional or local products commonly used to improve diet quality among pregnant women and/or young children (the specific comparator product used to set starting bids in Ghana was soybean flour, commonly sold by nurses at prenatal clinics, whereas in Malawi, it was a corn–soy blend called Likuni Phala, designed for children aged 6 months and older). Given that SQ‐LNS are meant to be consumed daily for many months, after respondents reported their maximum WTP for a day’s supply, they were asked follow‐up questions to elicit WTP for the product throughout the relevant time period (i.e., throughout pregnancy or throughout the first 6 months postpartum for SQ‐LNS‐P&L and from 6 to 18 months of age for SQ‐LNS‐Child). In Ghana, we analysed both stated maximum WTP for a day’s supply and stated long‐term WTP throughout the period. An error in the printing of the WTP surveys in Malawi rendered the estimates of long‐term WTP unreliable, so the Malawi analysis is limited to WTP for a day’s supply. To shed light on the factors that influence WTP for SQ‐LNS over the course of a child’s critical window of nutritional vulnerability, we combined the WTP data with household demographic and socioeconomic data, maternal and child morbidity data, as well as birth outcome and child growth data. The covariates used in our regression analyses are defined below and in Table A2 in the Supporting Information, and the average value of each covariate by round is in Supporting Information Tables A4 and A5. A household asset index was constructed using principal components analysis to combine data collected within a few months of enrolment on ownership of a set of assets, housing characteristics, and water and sanitation sources (Vyas & Kumaranayake, 2006). The Household Food Insecurity Access Scale Score is an indicator of a household’s level of food insecurity and was based on the Household Food Insecurity Access Scale (Coates, Swindale, & Bilinsky, 2007). Each household was assigned a score between 0 and 27 on the basis of how frequently the household experienced each of the nine food insecurity conditions in the 4‐week period prior to the interview; a higher score indicates higher food insecurity. Maternal morbidity data were collected at biweekly home visits during pregnancy and at weekly home visits for the first 6 months postpartum. Mothers were asked to recall the number of days in the past week (Ghana) or past 2 weeks (Malawi) in which they experienced each of a range of morbidity symptoms. Child morbidity data were collected at weekly home visits from birth to 18 months of age. With the aid of a morbidity calendar, specific dates in the previous week in which the child experienced each of a range of morbidity symptoms were recorded. Among the range of maternal and child morbidity symptoms available in the data, we selected a subset to include in our analysis primarily based on two criteria: (a) a parent or guardian might correlate the morbidity symptom with the need for or side effects associated with SQ‐LNS, and (b) there was sufficient variation in the data. Morbidity variables were defined as dichotomous indicators of whether the mother or child experienced the morbidity symptom for one or more days during the reference period (reference periods defined in Table A3 of the Supporting Information). The random assignment of mothers and their infants to receive SQ‐LNS allowed us to assess whether gaining first‐hand experience using them had an impact on stated WTP for SQ‐LNS. For the pregnancy and child periods, where we had up to two observations per respondent, we estimated a random effects tobit model (separately for each period) for i = 1 , 2 , … , N survey respondents and for t = 1 , 2 rounds of WTP data collection for latent variable yit* as (Cameron & Trivedi, 2010) where yit=yit*ifyit*>00otherwise. The dependent variable, yit, was stated WTP in 2011 US dollars for respondent i at time t. It was observed at its true value if WTP was greater than zero and censored at zero otherwise. LNSi was an indicator variable equal to one if the mother–infant dyad in respondent i’s household was randomized to receive SQ‐LNS and zero otherwise. The vector Tit comprised time‐varying controls (passage of time from enrolment/birth to WTP survey administration and indicators of randomized starting bid). The parameter αi was a respondent‐level random effect, and εit was an idiosyncratic error. Because the error was likely correlated over time for a given respondent, standard errors were bootstrapped to account for clustering at the level of the respondent. For the postpartum period in which there was only one observation per respondent, we used a tobit model with robust standard errors to estimate the effect of intervention group on WTP with the same set of controls as in Equation (1). In all models, heterogeneity over time, by survey respondent and by maternal parity, was assessed using interactions with intervention group. To estimate the association between stated WTP and the predicted correlates for the pregnancy and child periods, we extended Equation (1) to include a set of time‐varying covariates (e.g., maternal and child morbidity) in the vector Xit, and time‐invariant covariates (e.g., infant gender) in the vector Zi and estimated the following random effects tobit model The vector Tit again comprised time‐varying controls, in this case the passage of time from enrolment to WTP survey administration (pregnancy period) or birth to WTP survey administration (postpartum and child periods), the total number of days in the morbidity reference periods, and indicators of randomized starting bid. For the postpartum period, we estimated the correlates of WTP using a tobit model with robust standard errors. We also assessed the sensitivity of our regression results to the way the morbidity variables were defined (dichotomous vs. continuous) and the length of the morbidity reference periods. Sensitivity analysis results for each period are available in the Supporting Information.