Kohler | Statistics in News

Statistics in the News: Chapter 15 Analysis of Variance

Comparing the Effectiveness of Insect Repellents

Insect-transmitted disease remains a major source of illness and death worldwide. To give just two examples, consider that mosquitoes alone transmit disease to more than 700 million persons each year, while malaria kills 3 million persons annually. In the United States, thousands are falling victim to eastern and western equine encephalitis and ever more people in ever more states are being infected and die from the West Nile virus, also transmitted by mosquitoes.

Protection against mosquito bites is best achieved by avoiding infected habitats and wearing protective clothing, but that's not feasible for everyone. That brings us to insect repellents. In the United States, such readily available commercial products include synthetic chemicals containing DEET (officially called N,N-diethyl-3-methylbenzamide), various plant-derived essential oils, and even repellent-impregnated moisturizers and wristbands. Two researchers, Mark S. Fradin and John F. Day, recently investigated which of these products provide reliable and prolonged complete protection from mosquito bites. With the help of 15 volunteers, they tested a number of alternative products in a controlled laboratory environment, while holding constant the species of the mosquitoes, their age, their degree of hunger, the humidity, the temperature, and even the light-dark cycle.

Selected results from their two-way analysis of variance (plus Tukey's HSD tests) are summarized in Table A.

TABLE A Protection Times of Insect Repellents

*Major ingredient DEET

Conclusion: DEET-based products provided complete protection for the longest duration. Higher concentrations of DEET provided longer-lasting protection. Botanical repellents (based on cedar oil, eucalyptus oil, geranium oil, lemongrass oil, peppermint oil, soybean oil, and such) provided less protection. Repellent-impregnated wristbands offered no protection.

Source: Adapted from Mark S. Fradin and John F. Day, "Comparative Efficacy of Insect Repellents Against Mosquito Bites," The New England Journal of Medicine, July 4, 2002, pp. 13-18.