Demand and use of fortified infant cereals: Willingness to pay and substitution for other foods

This market experiment is part of a larger study entitled "Food Quality and Child Diets" at our study site. That study includes a marketplace survey, during which the interviewer will conduct a discrete choice experiment to elicit respondents' marginal rate of substitution (MRS) between a hypothetical fortified cereal, a plain maize porridge, and complementary foods made of greens, beans and other nutrient-dense family foods. Before the choice experiment, the interviewer will read one of two randomly assigned descriptions of the fortified cereal, to test for significant differences in MRS caused by how the fortified food is described in its marketing messages or label claims. Following the choice experiment, the interviewer will also conduct a random-price auction to elicit respondents' willingness-to-pay (WTP) for actual infant foods available in a variety of locations around the study sites.

The discrete choice experiment elicits respondents' preference between combinations of foods that would be cooked and fed to the child at home during or between family meals. Options are represented by photos of local dishes. The choice is hypothetical but does provide a realistic description of food options likely to be available in the respondent's home. In this experiment, respondents state their choice between two options, where each is a combination of either: (1) a double or a single portion of plain maize porridge, plus (2) a double or a single portion of a nutrient-dense family food, with or without (3) a single portion of a fortified infant cereal which is darker in color than the maize porridge. We restrict choices to options that have either 3 or 4 portions in total, so that only four choices are needed to make a full factorial design. We then replicate those four choices with three different nutrient-dense family foods, for a total of 12 choices that appear in random sequence. Prior to this choice experiment, our intervention concerns how the photograph of fortified infant cereal is described. Treatments are randomly assigned and not known to either the interviewer or the respondent until they reach that stage in the interview script. At that point, in the control arm, fortified cereals are described as "made especially for infants, with more nutrients than ordinary maize." In the marketing treatment, fortified cereals are described as "made especially for infants, with many of the nutrients in greens, beans, fruits & vegetables". These statements correspond to the two main types of marketing and product packages currently observed for a variety of fortified infant cereals sold around the world.

The random-price auction follows Becker, Degroot, and Marschak (1964), eliciting WTP for a real product that could actually be sold to the respondent during the interview. The interviewer invites the respondent to state the maximum price at which she would purchase the product if it were for sale, and later draws a random price at which the sale occurs if that randomly-drawn price is equal to or below the respondent's stated WTP. This mechanism is known to elicit bids that are unbiased estimates of the respondent's actual market intentions. To elicit bids for multiple products without satiation, we solicit bids for plain cereal grain and all of the different fortified infant cereals available in local markets, and then randomly select one for which a price is randomly drawn to determine the sale. Such an auction serves essentially as a randomized double-blind experiment in which the randomized component is the price at which the respondent is able to purchase the product in question. In the setting of our trial, respondents will typically have come to the market without any cash beyond what is needed for that day's planned purchases. To ensure that respondents are able to make bids, they will be given an unconditional cash grant during the informed consent phase of the interview. This ensures that all respondents are able to participate in the auction, if they so choose, and decide whether or not they wish to make an offer to purchase each type of food. Any difference in behavior between WTP from a grant versus earnings will be absorbed by also soliciting WTP for plain maize, so that the endpoint of interest is the difference rather than the level of WTP.

2018-06-18

2018-07-25

Our primary outcomes of interest are
1) respondents' willingness to pay (WTP) for each infant food, in local currency units per package, and
2) respondents' marginal rate of substitution (MRS) between a porridge made with fortified infant cereal and either plain maize porridge, or a nutrient-dense family food.

Respondents' WTP is the difference between the respondent's bid for the infant food and their bid for the plain maize, so as to focus on the price premium they are willing to offer. The estimated MRS in this population is the ratio of coefficients on indicator variables for whether the infant food is present, and for the double (vs. single) portion of the other food in question. That other food could be either plain maize porridge or one of three nutrient-dense family foods.

Our study questionnaire also includes standard 24-hour recall modules for infant feeding practices and maternal diet quality, from which we can construct:
(a) Child diet diversity scores (CDDS), and a
(b) Minimum diet diversity for women (MDD-W) indicator for the respondent.

In addition to standard CDDS and MDD-W indicators following FAO protocols, our survey includes a module regarding respondent's knowledge and experience with contaminants in food, as well as demographic questions about the respondent, her child and her household. These will permit secondary analysis for the determinants of maternal and child diet quality, as context for our primary aims regarding WTP and MRS for fortified infant foods.

Our population of interest is mothers or caregivers of at least one children between the ages of 6-24 months who are actual or potential buyers of infant foods. To obtain a sample that is representative of all shoppers, we will approach potential participants near entrances and exits around 15 public marketplaces that are purposely selected to represent places frequented by higher, medium and lower-income consumers, at varying locations that serve urban, peri-urban and also rural areas. Enumerators will be instructed to approach the potential participants based on the next person to walk past a landmark at a designated time. Potential participants are defined as women who appear to be between the ages of 18 and 35, and therefore likely to meet our inclusion criterion of being 18 or over and responsible for feeding at least one infant between 6 and 24 months of age. All others are to be excluded. This market intercept approach is designed to generate a purposive sample of actual or potential shoppers at each marketplace who are currently feeding an infant of relevant age. Analysis will include statistical controls for each location, day of the week and time of day to account for selection into time and place of shopping, as well as the identity of the enumerator to account for experimenter fixed effects.

Once approached, potential participants are offered informed consent to participate in a market survey that will offer them the opportunity to purchase a packet of an infant food if they so wish. The survey begins with demographic questions, and dietary recall modules for infant feeding and the respondent's own intake over the previous 24 hours. We then introduce the discrete choice experiment, which begins with the randomly assigned marketing treatment by which the fortified infant cereal is described. Following that we conduct the BDM auctions, practicing first with bids and random-price sales for a bar of soap before proceeding to bids for maize and each kind of packaged food, then a random draw for which could be bought, and random draw for its price to determine whether that item actually is purchased. We will test for impacts of the marketing treatment on bids in the BDM auction, but do not expect significance the auction uses real products that already have their actual packaging materials and label claims. The content of the treatments, the choice experiment and our basic analysis plan are described under Experimental Details.

Randomization of potential sale price in the BDM auction is done by inviting the respondent to draw a price card from a cup held above eye level.

Randomization of marketing treatment before the discrete choice experiment is done in office by computer, setting the treatment for each successive survey by serial number. Assignment is double-blind until the interview reaches that stage of the survey, at which point the enumerator's tablet reveals which script will be read to the respondent.

Randomization of the sequence of choices made is done via creation of four decks of photo cards, each of which provides a different sequence of 12 choices with different A-B assignments for use by the interview to elicit the respondent's preference between options A and B in each of the 12 choices.

Individual

No

None, but we will use fixed effects to address variance associated with 15 marketplaces and 4 enumerators as well as day of the week and time of day

360 respondents (mothers, or other caregivers with primary responsibility for feeding at least one infant who is 6-23 months of age)

180 in the control arm, for whom the fortified cereal is described as "made especially for infants, with more nutrients than ordinary maize."

180 in the treatment arm, for whom the fortified cereal is described as "made especially for infants, with many of the nutrients in greens, beans, fruits & vegetables".