Testing the effects of nutrient deficiencies on behavioral performance.

The association between specific nutrient deficiencies and poor performance on behavioral tests has been documented for several nutrients. The determination of causality, however, remains elusive. This paper presents the essential criteria for a valid test of causality. Findings from experimental studies in which a nutritional treatment was randomly allocated can be summarized in a statistical statement about the probability that the nutrient treatment caused the behavioral response. Criteria for assessing the internal validity of these studies are examined in terms of whether alleviation of a nutrient deficiency did or did not produce a detectable behavioral response. The plausibility of such a causal inference is dependent on its congruency with known or theorized biological and behavioral mechanisms. External validity describes the extent to which inferences from internally valid studies may be applicable to other populations or circumstances. In addition to these scientific considerations, some of the ethical issues of nutrient-treatment trials are also discussed. All of these considerations provide a better basis for judging whether public health action would be worthwhile than do observed associations that could actually be due to other causes.

Community-based health workers: head start or false start towards health for all?

Health service delivery programs using minimally-trained community-based health workers (CHWs) have been established in many developing countries in recent years. These programs are expected to improve the cost-effectiveness of health care systems by reaching large numbers of previously underserved people with high-impact basic services at low cost. The reported experience with these programs has been mixed, raising questions about whether the community health worker is an optimal vehicle for extending primary health care. This review of six large-scale community-based worker programs suggests that they have succeeded in some of their objectives but not in others. CHWs increase the coverage and equity of service delivery at low cost compared with alternative modes of service organization. However, they do not consistently provide services likely to have substantial health impact and the quality of services they provide is sometimes poor. Large-scale CHW systems require substantial increases in support for training, management, supervision, and logistics. The evidence suggests that, in general, their potential has not been achieved in large routine programs. Further development of these programs is needed to reinforce their successes and assure that they are adequately supported as an integral component of the basic health system.