The central impression from the review of the research literature on indoor air pollution as a cause of ARI among children in developing countries is the imbalance between the number of articles reporting on original, empirical research, on the one hand, and the number of calls for research, reviews and projections based on those articles, on the other. Figure 2 illustrates the discrepancy between the research that is done and the global needs for research, where the smallest proportion of the research is done where the results could potentially have the greatest impact on the health of populations. This is an illustration of what has been labeled the 10/90 gap (ie, that 10% of health research resources are said to go to 90% of the disease burden).
A majority of the empirical studies indicate that increased ARI risk is associated with indicators— measurement or proxy—of individual exposure to indoor air pollution. Not all of the studies are reported in such a way that it is possible to draw clear conclusions, even allowing for small samples, but results from only one study are negative. One study is inconclusive because of homogeneity of exposure and small sample size. Otherwise, the tendency is consistently toward an association. Recurring problems are small samples and the fact that studies were not primarily designed to address the ARI/air pollution question, but included data on air pollution indicators for at least a subset of the study subjects. However, several have a well-planned design and use plausible methods for diagnosis and exposure classification.