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Observation (placebo) effects
Improved hygiene knowledge and practices and lower diarrhoeal morbidity compared with the baseline samples were observed in the 1986 control group as well as in the intervention group, although they were substantially less pronounced. This may be due in part to the high level of education and socioeconomic status of the 1986 control sample. Our finding that the parents' education was significantly associated with hygiene knowledge and practices is consistent with other studies [29-39]. It is probably more attributable, however, to the effects of intensive observation, which functioned as a placebo effect at the control site.
The behavioural observation team visited each family in the control-site sample every other day for six months and recorded routine eating or feeding events, food preparation, other child-care practices, and personal (face, hands, legs, between fingers, clothes), ground, and latrine cleanliness and defecation events . To observe how mothers cleaned their babies after defecation, simulations were constructed using wheat-flour paste as faeces placed on the baby's posterior and on the ground. The mother was requested to clean up this paste as if she were cleaning faeces after defecation. The presence of paste remaining on the child and mother and on the ground was physically checked and recorded. Mothers also answered many queries about their hygiene and cleanliness practices.
A visit to these rural areas by city people or government officials usually is rare and considered special. The regular visits and continuous presence of an energetic and well-educated research team may have had a positive effect on the behaviours of those being observed. Although the field team was carefully trained not to give hygiene education, explain the purpose of the study, or express approval or disapproval of the behaviours they observed, the very nature of the questions they asked and the types of observations they made, as well as their unintended expressions or body language, could have provided villagers with feedback regarding the observers' values and intentions.
The compounded effects of all these factors may have resulted in behaviour change in the desired direction. In fact, we considered observational research to be an appropriate placebo intervention, since even the most ineffective of interventions would probably have exerted an influence through social approval of cleanliness.
Intervention effects and measuring problems
While the scores for the mothers' hygiene knowledge and practices were significantly higher and the children's growth status was better for the 1986 intervention sample than for the baseline samples or the 1986 control sample, this relatively low-cost cross-sectional study design did not detect significant differences in diarrhoeal morbidity. Significant differences that could not be measured by this evaluation, however, were documented in a study using longitudinal methods reported elsewhere . From March through June the intervention site had significantly lower diarrhoeal prevalence than the control site, with the highest differences in one of the peak seasons (April-May). In general, we suspect that seasonal variability in diarrhoeal disease is too large to permit cross-sectional evaluation of rate changes. Even if repeat measurements are made at exactly the same time each year, seasonal trends may peak at different times in different years.
Two other factors possibly further obscuring the intervention effect were a two-month delay in administering the baseline survey at the intervention site, yielding a diarrhoeal rate not strictly comparable at the starting point, and the effect of faeces-pit flooding at the intervention site during the final survey.
In Bangladesh, the climate affects morbidity greatly [40, 41]. In 1985, when the baseline survey was carried out at the control site, a major outbreak of diarrhoea appeared to have occurred during the last two weeks in July when rising water levels contaminated water supplies. About two months later, the baseline survey at the intervention site was administered during a time of relatively dry weather when diarrhoeal prevalence among the sample children was low. The contrast in diarrhoeal rates between the control and intervention baseline samples (about 3:1) probably reflects seasonal conditions. A longitudinal study in Bangladesh documented that the diarrhoeal rate in August was three times higher than in September . Therefore, the baseline survey results are not comparable between the intervention and control sites.
Although we attempted to estimate the diarrhoeal rate at the intervention site at the time of baseline at the control site, it has often been reported that estimates based on recalls longer than two weeks are inaccurate. In fact, long-term recall underestimates actual rates by as much as 44% . We believe that our estimate of the diarrhoeal rate two months prior to the interview was probably much less than the actual rate. If our estimate of the baseline diarrhoeal rate (56%) was similar to the rate at the control site but lower than the actual rate, it supports our conclusion. Moreover, the longitudinal study of the same intervention  suggests the same conclusion.
A major failure to overcome problems of flooding diminished the real effect of the intervention at its end. One of the messages recommended depositing children's and animal faeces in a pit at the edge of the courtyard. During floods, this collection of faeces contaminated the source of bathing, washing, and cocking water at the intervention site and may have caused an increase in diarrhoea. A longitudinal study at the intervention site  found very high rates of diarrhoea in children whose families had flooded faeces pits. In contrast, at the control site faeces were usually thrown into the fields and dried up in the sun (N.U. Ahmed, personal observation, 1986), and so that site had lower levels of contamination than the intervention site.
Moreover, analysis of the baseline survey data reported elsewhere  showed that households with no latrine facilities used the field for defecation, and their children had fewer episodes of diarrhoea than children of households with latrines. This led us to believe that this specific intervention was detrimental in flood conditions. In future, it could be recommended that the faeces in the pit should be covered with dust or soil in layers every few days and then, when a given level is reached, that the pit should be filled with enough soil to seal it and a new pit made for further use .
There is commonly a positive association between the socio-economic condition of the family and weight for age [34-37]. In this study, however, despite the intervention families having lower socioeconomic conditions, their children displayed higher growth status.
In addition to protecting growth through less diarrhoea, the intervention taught mothers to practise better food hygiene, which may have reduced the level of contamination and hence led to better absorption of nutrients by the children. Food hygiene intervention, however, may have had a negative effect on height for age caused by the successful campaign to reduce bottle-feeding , which inadvertently also reduced milk consumption.
Unhygienic practices can be altered by a combination of mothers' proper understanding of germ theory, of the detrimental effect of unhygienic behaviours on health, and of ways and benefits of hygienic practices. Although this conclusion is consistent with another study , it may be possible for community mothers to imitate the hygiene practices of project workers and volunteer teachers without understanding germ theory. Analysis of the same intervention data , however, found a highly significant positive correlation between the mothers' understanding scores and their rates of adoption of hygiene practices as well as their cleanliness scores, after controlling for mothers' education, mothers' age, children's sex and ages, household possessions, and agricultural wealth. We believe that if the hygiene-related messages are need-oriented, specific, simple, feasible, and suitable for the particular setting, the potential for their adoption among the target population tends to be very high.
Almost all the intervention recommendations were accepted by 90%-100% of the target-community mothers except for the use of tube-well water for cooking (25%), feeding no leftover food to the baby (75%), boiling the feeding bottle and nipple (50%), and replacing old, sticky bottle nipples (67%). These recommendations were less acceptable mainly for economic reasons. Food cooked with tube-well water was reported to taste of iron, discolour, and spoil faster. Many families could not afford to cook fresh food frequently or to avoid giving leftover food to the children. The failure of these aspects of the intervention suggests problems of poverty that may not be solved by education alone .
The findings of this study lead us to conclude that the higher levels of mothers' education, better socioeconomic conditions, and intensive observations at the control site resulted in favourable outcomes there. Although these better conditions could have worked against our finding a large difference between the sites, nevertheless the intervention both compensated for the less favourable conditions and produced better outcomes.
Our conclusion regarding evaluation measures is that the repeat cross-sectional survey may be adequate for measuring relatively stable outcomes such as knowledge, practices, and cumulative growth status. It is not adequate for measuring morbidity, which fluctuates seasonally. It may be recommended that recall data collected at weekly or at least two-weekly intervals will provide adequate measures of morbidity.
The authors wish to thank Ms. Helen C. Armstrong for her technical and editorial comments on the manuscript. Their appreciation goes to the reviewers for valuable comments. They also thank the village volunteers, workers, mothers, and leaders for their active participation and taking responsibility to solve their community problems, and Ms. Linda Vogel of the Office of International Health of the US Public Health Service for her support.
This study was conducted as part of a Positive Deviance Study of Maternal Hygiene Behaviors and Psychosocial and Environmental Factors Related to Diarrhoeal Infection and Growth of Infants, under Contract No. 282-86-0011 with the Office of International Health of the US Public Health Service, with funding under RSSA No. BAS-0249-R-HI-4208 from the Asia Bureau of the US Agency for International Development.
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