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ARTICLES: Thomas J. Sandora, Mei-Chiung Shih, and Donald A. Goldmann Reducing Absenteeism From Gastrointestinal and Respiratory Illness in Elementary School Students: A Randomized, Controlled Trial of an Infection-Control Intervention Pediatrics 2008; 121: e1555-e1562 [Abstract] [Full text] [PDF]

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Real Significance of the Reduction in Absenteeism

John J Li, Craig Hedberg   (6 June 2008)

No Placebo Used in Trial

Anthony W Hughes   (2 July 2008)

Real Significance of the Reduction in Absenteeism 6 June 2008
John J Li, Doctoral Student Department of Epidemiology and Community Health, University of Minnesota School of Public Health, Craig Hedberg Send letter to journal: Re: Real Significance of the Reduction in Absenteeism lixxx607{at}umn.edu John J Li, et al.	In a recent article in Pediatrics, “Reducing Absenteeism From Gastrointestinal and Respiratory Illness in Elementary School Students: A Randomized, Controlled Trial of an Infection-Control Intervention”, Sandora and colleagues stated that “a multifactorial intervention including hand sanitizer and surface disinfection reduced absenteeism caused by gastrointestinal illness in elementary school students” (1). While we applaud all efforts to improve hygiene in schools, we question both the validity and importance of their findings. To begin with, the authors used a clustered randomized design with teams as the unit of assignment. This is also commonly called a group randomized trial (GRT). We agree with the authors that a general estimating equation with teams as a random effect can be used to analyze this data, but it has been noted that in situations where there are less than 40 groups the sandwich estimator used in GEE is biased downward (2, 3). This means that without proper correction of the variance you will get an incorrectly low estimate of your standard error. It is unclear if the authors accounted for this, and in their later estimates of sample size it appears they didn’t. The authors used the total number of students in their power calculations without consideration that the actual unit of randomization was the team. There was no mention in the power calculation of adjusting for the intraclass correlation, or the variance inflation factor which is needed when randomization is at the group level (4). This casts some doubt over the p-values of the intervention effect that they found. However, even if we accept the validity of their effect measures, the difference in absenteeism rates between the two groups was 3.7 absences per 1,000 student-days of observation. This translates into a predicted 22 fewer absences due to gastrointestinal illnesses in the treatment group over the study period. How important is this? In public schools, increased absenteeism reduces state subsidies. Based on state allocations in Minnesota, the value of these absences would be around $1,200. However, the costs of 205 containers of sanitizing wipes and 70 bottles of hand sanitizers appear to be in the same ballpark. Finally, the results of environmental sampling do not provide compelling evidence for a clear and consistent effect from the use of these products in the classroom. During week 1 the treated classrooms clearly had fewer samples positive for norovirus and lower heterotrophic plate counts. It would be nice to credit these results with the lowered rates of gastrointestinal illness in the treatment classes. However, doing so is not that straightforward. During week 2 the control rooms were cleaner than the intervention rooms had been during week 1. During week 4, both control and intervention rooms resembled the control rooms from week 1. No explanation is offered for the instability of the environmental sampling results, but they suggest that the use of hand sanitizers and surface disinfectants was not the primary determinant of the hygiene levels in the classroom. Working out the fine details of how the use of hand washing and personal hygiene measures can reduce absenteeism in schools is a difficult task. Sandora and colleagues have demonstrated an approach that could be useful on a larger scale with better linkage between environmental monitoring and observed patterns of absenteeism. 1. Sandora TJ, Shih MC, Goldmann DA. Reducing Absenteeism From Gastrointestinal and Respiratory Illness in Elementary School Students: A Randomized, Controlled Trial of an Infection-Control Intervention. Pediatrics 2008;121(6):e1555-e1562. 2. Murray DM, Varnell SP, Blitstein JL. Design and analysis of group- randomized trials: a review of recent methodological developments. Am J Public Health 2004;94(3):423-32. 3. Murray DM. Design and analysis of group-randomized trials. New York: Oxford University Press; 1998. 4. Hsieh FY. Sample size formulae for intervention studies with the cluster as unit of randomization. Stat Med 1988;7(11):1195-201. Conflict of Interest: None declared
No Placebo Used in Trial 2 July 2008
Anthony W Hughes, economist Concerned citizen Send letter to journal: Re: No Placebo Used in Trial thughes{at}economy.com Anthony W Hughes	I strongly suspect that these findings are due to a placebo effect. It would have been straightforward to create a wiping product with no active ingredients for use by the control group and then to disguise this fact from the subjects. A "sugar pill" if you will. In circumstances like these, where subjects and their parents have strong priors about the efficacy of cleaning products (fuelled by mass advertising by the study's sponsor), conducting a study that fails to consider the psychology of the subjects is disingenuous and unscientific. Conflict of Interest: None declared

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