Int. J. Environ. Res. Public Health 2009, 6 697 The sample was stratified by the health region of residence, and post-stratified by gender (in order to take into account the greater difficulty in reaching men [17]). Due to operational and budgetary constraints, we used random household sampling instead of a within-household sampling. The respondents were contacted by a polling firm from random digit dialing of published residential telephone numbers (confidential numbers were not used due to ethical considerations). The study obtained ethical approval from Laval University’s Comité d’éthique de la recherche avec des êtres humains. The sample size was calculated using 2001 survey data [18], for a 95% confidence level and a precision level of 1.5%, for a 4-point Likert-type scale including 6 items [19]. From the initial sample (n = 4,000), 2,570 completed the questionnaire (Table 1), for a response rate of 70%. The percentage of respondents and non-respondents were similar across health regions of Québec (p = 0.4). Table 1. Sample description. 4,000 129 140 3,731 1,161 2,570 70.0% 89 13 27 12 70 54 4 646 155 129 3 11 217 A) Initial sample B) Not-valid numbers C) Numbers excluded from sample Effective sample (A minus B+C) Non completed interview No service Non-residential Fax/modem/cellular/paget Foreign language Completed quota (for stratified sampling) Non qualified (ex. disease, age under 18 years) Bad quality of communication Refusal No response Answering machine Occupied Incomplete Not interviewed because data collection ended before the date of the appointment made with the polling firm D) Completed interviews Response rate (C+D/A-B) 2.2. Data Collection Method The polling firm collected individual responses by telephone (average duration: 20 minutes), seven days a week, from 9:30 a.m. to 9:30 p.m., using a computer system that allowed the order of the questions (essentially closed) to be randomly redistributed. More precisely, collection (from 15-09- 2005 to 25-10-2005) allowed information to be gathered on socio-demographic characteristics, health status, dwelling, region of residence, the use of an automobile and a remote starter during the whole winter, consultation of weather and smog reports, as well as on perceptions and beliefs relating to climate change and the behaviors adopted during a period of intense cold. The questionnaire was developed according to the following six steps: 1) identifying the important issues to consider in the exploratory interviews [20] based on the literature on health and climate change; 2) conducting 21 face-to-face pilot interviews (average duration: two hours), mainly to verify the understanding of