NUTRITIONAL IMPACT OF SUPPLEMENTATION IN THE INCAP LONGITUDINAL-STUDY- ANALYTIC STRATEGIES AND INFERENCES

From 1969 to 1977 a supplementation trial was conducted in Guatemala t o ascertain the effects on physical and behavioral outcomes of improve d nutrition in pregnant women and in preschool children. This paper re views different strategies to analyze the effect of the intervention o n physical growth. One strategy compares outcomes in two villages that were randomly allocated to receive Atole, a supplement containing hig h amounts of protein and energy, with values in two other villages tha t received Fresco, a beverage containing no protein and little energy. Both supplements contained micronutrients. This comparison of village means gives a probability significance statement (P < 0.005) that the difference in growth was because of the supplement intervention, alth ough it does not specify the aspect of the intervention that caused th e effect. Complementary strategies increase the credibility that the e ffect of the supplement was nutritional. Thus, analysis of the dose re sponse with increasing supplement intake within the villages excludes the possibility that the above findings were the result of knowing whi ch villages received which supplement (i.e., measuring biases). A grea ter effect in those most likely to respond nutritionally also increase s the credibility that the mechanism was nutritional. In studying othe r behavioral and biomedical impacts of this supplementation interventi on, analyses for credibility should always be included.