Prevalence of Headache among Handheld Cellular Telephone Users: Response.

We would like to clarify that at no time was our study (1) "based on [Hocking's] data in a report of a case series of symptomatic users...." When we were discussing which factors (symptoms) to study among hand-held cellular telephone users, Hocking's paper (2) is only one of many to which we referred.

Because ours was a community-based study (1), we examined "specific CNS symptoms among handheld cellular telephone users compared to nonusers." Headache is only one of the symptoms we studied. We used the International Headache Society Classification because it is commonly used in publications related to headache; the use of this classification would also enable standardization and comparison with other papers. Because our definition is different from that of Hocking, we certainly cannot analyze "unilateral to side of use" because this information was not determined in our study. We had no intention of confirming or refuting Hocking's report. In fact, we made no reference to Hocking's paper (2) in the "Discussion" of our paper. Therefore, we do not see how our definition of headache "would lead to imprecision in case ascertainment and hence a minimal estimate of the risk."

Sin-Eng Chia
Hwee-Pin Chia
Department of Community Occupational
& Family Medicine
National University of Singapore
Singapore, Republic of Singapore
E-mail: [e-mail]

REFERENCES AND NOTES

(1.) Chia SE, Chia HP, Ten JS. Prevalence of headache among handheld cellular telephone users in Singapore: a community study. Environ Health Perspect 108:1059-1062 (2000).

(2.) Hocking B. Preliminary report: symptoms associated with mobile phone use. Occup. Med 48(6):357-360 (1998).