Correspondence/Rebuttal pubs.acs.org/est
Comment on “Randomized Intervention Study of Solar Disinfection of Drinking Water in the Prevention of Dysentery in Kenyan Children Aged under 5 Years” n their recent paper du Preez et al. report the “first trial to show evidence of the effects of SODIS on childhood anthropometry, with a statistically significant difference in the height-for-age of children on SODIS (0.8 cm 95% CI 0.7 cm to 1.6 cm, P = 0.031) compared with children in the control group”.1 The authors claim that their findings should then alleviate concerns that the reported lower rates of diarrhea in users of SODIS is largely or totally due to reporting (courtesy) bias. In making this claim the assumption is that that measurement of height of children or length of babies is an objective outcome measure. It is not. In a systematic review on the lack of blinding or allocation concealment, Wood and colleagues gave good definitions of what are subjective and objective outcome measures.2 They based their definition on the extent that outcome assessment could be influenced by investigators’ judgment. They defined objectively assessed outcomes as all cause mortality, measures based on a recognized laboratory procedure, or certain other outcomes that were concerned with childbirth. Subjectively assessed outcome measures were defined as those that included patient reported outcomes (such as self-reported diarrhea), and physician assessed disease outcomes (such as vascular events, pyelonephritis, or respiratory distress syndrome)”. Within their definition height/length measurement is clearly a subjective outcome measure. Measurement of height or length in young children is notoriously difficult and with unstandardized assessors, as in the du Preez study, the interobserver technical error of measurement (TEM) is about 1.4 cm3 greater than the reported difference between the two populations. Of particular concern is the comment in the paper that “field staff reported in feedback sessions that they were disappointed by the lack of any apparent difference in the growth of children in the SODIS arm, making biased reporting less likely.” The fact that field workers wanted a positive outcome makes reporting bias much more likely with a subjective measure such as height. Even an apparently objective measurement such as how many households have SODIS bottles exposed to the sun is open to substantial reporting bias. In a recent paper, it was shown that SODIS-implementing staff reported a median proportion of 75% of households with SODIS bottles exposed to the sun, while the independent assessors reported an overall median of just 33%.4 Another concern is that the authors state that “anthropometry was not the main focus of the study” suggesting that an impact on height was not one of the primary hypotheses. Significant association in epidemiological studies may arise by chance and consequently one has to be very cautious about drawing conclusions about causal association based on associations between an intervention and outcome measures that were not the primary focus of the study. So in conclusion, the recent study by du Preez and colleagues cannot be used to prove whether or not SODIS reduces
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diarrheal disease or improves growth. The apparent increase in height in SODIS users in this study is almost certainly an artifact from using a subjective and relatively imprecise measure in an unblinded study.5,6 The study of du Preez et al. is an example of a wider trend in developing country research for persistence with studies more suitable for initial hypothesis generation and screening when the real need is for studies than can give a more unequivocal indication of cause and effect or provide better quantification of effect sizes.
Paul R. Hunter* The Norwich School of Medicine, University of East Anglia, Norwich NR4 7TJ, U.K.
Jamie Bartram Water Institute, Gillings School of Global Public Health, University of North Carolina at Chapel Hill, North Carolina.
Sandy Cairncross
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London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, U.K.
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected].
REFERENCES
(1) du Preez, M.; Conroy, R. M.; Ligondo, S.; Hennessy, J.; ElmoreMeegan, M.; Soita, A.; McGuigan, K. G. Randomized intervention study of solar disinfection of drinking water in the prevention of dysentery in kenyan children aged under 5 years. Environm. Sci. Technol. 2011, 45, 9315−9323. (2) Wood, L.; Egger, M.; Gluud, L. L.; Schulz, K. F.; Juni, P.; Altman, D. G.; Gluud, C.; Martin, R. M.; Wood, A. J. G.; Sterne, J. A. C. Empirical evidence of bias in treatment effect estimates in controlled trials with different interventions and outcomes: Meta-epidemiological study. Brit. Med. J. 2008, 336, 601−605. (3) Jamaiyah, H.; Geeta, A.; Safiza, M. N.; Khor, G. L.; Wong, N. F.; Kee, C. C.; Rahmah, R.; Ahmad, A. Z.; Suzana, S; Chen, W. S.; Rajaah, M.; Adam, M. Reliability, technical error of measurements and validity of length and weight measurements for children under two years old in Malaysia. Med. J. Malays. 2010, 65 (Suppl A), 131−137. (4) Christen, A.; Pacheco, G. D.; Hattendorf, J.; Arnold, B. F.; Cevallos, M.; Indergand, S.; Colford, J. M.; Mäusezah, D. Factors associated with compliance among users of solar water disinfection in rural Bolivia. BMC Public Health 2011, 11, 210. (5) Schmidt, W.-P.; Cairncross, S. Household water treatment in poor populations: Is there enough evidence for scaling up now? Environ. Sci. Technol. 2009, 43, 986−992. (6) Hunter, P. R. House-hold water treatment in developing countries comparing different intervention types using metaregression. Environ. Sci. Technol. 2009, 43, 8991−8997.
Published: February 2, 2012 3035
dx.doi.org/10.1021/es204500c | Environ. Sci. Technol. 2012, 46, 3035−3035
