Prevalence of Headache among Handheld Cellular Telephone Users in Singapore: A Community Study

Environmental Health Perspectives, Nov, 2000 by Sin-Eng Chia, Hwee-Pin Chia, Jit-Seng Tan

The objectives of our study, therefore, were to study the prevalence of specific central nervous system (CNS) symptoms among HP users compared to non-HP users and to determine the association of risk factors and CNS symptoms among HP users.

Methods

Study design and subjects. To reduce subject bias, we told subjects that we were studying the prevalence of headache and the associated risk factors in the community. Thus, study subjects were not aware that we were studying the effects of HP use and CNS symptoms.

We conducted a cross-sectional study in a housing estate (Bishan) in the northeastern sector of Singapore. The study location was chosen because of demographic factors. Because it is growing estate, established about 10-15 years ago, there would be a suitably large proportion of younger families. Therefore, we could find a respectable mix of HP and non-HP users there. It is a typical Singaporean urban area and reflects a typical Singaporean living standard.

Estimating the difference of prevalence of headache among HP users and non-HP users to be approximately 10% and an [Alpha] of 0.05, we needed approximately 800 individuals to achieve a power of 0.8 for the study. From our pilot study, the household and individual response rates were 60% and 70%, respectively. We also found out that the average household size, with eligible individuals, was three. These figures were used in our computation to determine the number of households (635) needed to obtain 800 individuals.

We used a one-stage random cluster sampling procedure to draw a random sample of 635 households, targeting at 800 individuals, from all of the Housing Development Board flats in Bishan, Singapore. The eligible subjects were all Singaporeans and permanent residents between the ages of 12 and 70 years who resided in Bishan during the time of the survey (12-16 January 2000) and who were healthy and had no known medical problems. The household participation rate was 66.6%, and the individual participation rate was 67.4%, giving an effective sample of 808 respondents. Participation rates for both households and individuals exclude subjects who could not be contacted and those who refused to participate.

Questionnaire. All respondents were interviewed by a team of trained medical students using a structured questionnaire (with English, Chinese, and Malay translation), which had been field-tested in a pilot study. Interviewers who were fluent in a particular language were asked to interview the respondents who spoke that language. The interview was conducted at the respondents' house with informed consent.

Components of the questionnaire. The questionnaire included a) personal information (age, sex, occupation, marital status, and ethnic group); b) questions on general health status and any diagnosed medical conditions; and c) nature and severity of CNS symptoms. We used a two-tier approach in our questionnaire to minimize recall bias. Before asking the individuals about the use of HPs, interviewers first asked about their headache problems in terms of frequency, nature, and severity. Because headache is a common public health concern and is a topic of interest among the public, the topic would engage participants in the survey but would mask the actual survey goal of determining the relationship of the symptoms with HP use.