|Positive Deviance in Child Nutrition - with Emphasis on Psychosocial and Behavioural Aspects and Implications for Development (UNU, 1990, 153 pages)|
The positive-deviance research approach falls within traditional epidemiological methods of studying prevention, and it is applicable to all types of diseases and risk factors. However, positive-deviance studies differ from the majority of epidemiological studies in three respects.
First, most epidemiological research focuses on identifying the agents and pathways of transmission that cause disease states and on preventing exposure to these agents and pathways. Positive-deviance research applies to cases where exposure already has occurred. It focuses on identifying sources and pathways of natural immunity or adaptive resistance. For example, positive-deviance research on AIDS (acquired immune deficiency syndrome) would work to determine why some individuals who have positive antibody tests to the AIDS virus do not come down with the disease and how others who are antibody positive can benefit from the same sources of resistance.
Second, the majority of epidemiological studies have yes/no outcomes. Positive deviance research, particularly in nutrition, tends to have a continuous range of outcomes. In most epidemiological research the individual either has an event or condition or doesn't have it (e.g. stroke, infection, heart attack, accident, burn, cancer, infant death). Such clean distinctions lend themselves to relatively simple retrospective case-control study designs.
Positive-deviant children, with respect to nutritional status or childhood illness, such as diarrhoea, do not fall into such either/or classifications. They rank at the high end of a continuous distribution of nutritional status or the low end of a distribution of sick days with diarrhoea, for example. Case-control methods that pool together the children at the worst end of the distribution (cases) and contrast them with a pooled group from the top (controls), as was done by Clemens and Stanton (1986) in a study of infant diarrhoea in Dhaka, Bangladesh, may lose critical information about individuals ranked intermediate between the cases and the controls. They also lose information from the variability between children within the top and bottom groups.
For example, a study of maternal feeding behaviours, directed towards 9- to 20 month-old children in Mexico, showed a highly significant positive correlation between active maternal feeding behaviours and growth status, when growth status was measured as a continuous variable (height-for-age). However, when tall children in the top third of the distribution (controls) were contrasted to short infants in the bottom third (malnutrition cases), the difference in active maternal feeding behaviour between the groups was much less significant (Zeitlin and Johnson, in progress). This drop in apparent significance occurred because the mothers of the tallest children were relatively less active in feeding them than those of children in the middle range. Examination of the top and bottom groups only would not have discovered this important information.
Third, positive-deviance studies tend to require complicated designs and analyses, because many psychological and behavioural factors contribute to resistance. Traditional epidemiological methods establishing the links between disease agents and disease states can be relatively simple. The main requirement for testing the relationship between dietary fat and breast cancer, for example, is to obtain large amounts of data on two variables: dietary intake of fat and breastcancer incidence. To identify the factors that protect women with high fat diets from developing cancer (positive deviance) would be much more complex and would involve psychological testing.