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9 August 2013

Methods to Calculate the Heat Index as an Exposure Metric in Environmental Health Research

Publication: Environmental Health Perspectives
Volume 121, Issue 10
Pages 1111 - 1119


Background: Environmental health research employs a variety of metrics to measure heat exposure, both to directly study the health effects of outdoor temperature and to control for temperature in studies of other environmental exposures, including air pollution. To measure heat exposure, environmental health studies often use heat index, which incorporates both air temperature and moisture. However, the method of calculating heat index varies across environmental studies, which could mean that studies using different algorithms to calculate heat index may not be comparable.
Objective and Methods: We investigated 21 separate heat index algorithms found in the literature to determine a) whether different algorithms generate heat index values that are consistent with the theoretical concepts of apparent temperature and b) whether different algorithms generate similar heat index values.
Results: Although environmental studies differ in how they calculate heat index values, most studies’ heat index algorithms generate values consistent with apparent temperature. Additionally, most different algorithms generate closely correlated heat index values. However, a few algorithms are potentially problematic, especially in certain weather conditions (e.g., very low relative humidity, cold weather). To aid environmental health researchers, we have created open-source software in R to calculate the heat index using the U.S. National Weather Service’s algorithm.
Conclusion: We identified 21 separate heat index algorithms used in environmental research. Our analysis demonstrated that methods to calculate heat index are inconsistent across studies. Careful choice of a heat index algorithm can help ensure reproducible and consistent environmental health research.
Citation: Anderson GB, Bell ML, Peng RD. 2013. Methods to calculate the heat index as an exposure metric in environmental health research. Environ Health Perspect 121:1111–1119;

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Information & Authors


Published In

Environmental Health Perspectives
Volume 121Issue 101 October 2013
Pages: 1111 - 1119
PubMed: 23934704


Received: 15 November 2012
Accepted: 7 August 2013
Published online: 9 August 2013



G. Brooke Anderson
Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA
Michelle L. Bell
School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut, USA
Roger D. Peng
Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA


Address correspondence to G.B. Anderson, Department of Biostatistics, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe St., Baltimore, MD 21205 USA. Telephone: (203) 508-2738. E-mail: [email protected]

Competing Interests

The authors declare they have no actual or potential competing financial interests.

Funding Information

Funding for G.B.A. and R.D.P. was provided by the National Institute of Environmental Health Sciences (NIEHS; ES019560, ES020152). Funding for M.L.B. was provided by the U.S. Environmental Protection Agency (RD 83479801) and NIEHS (ES019560, ES016317, ES019587, ES020152, ES021427).

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