Jarahi et al. BMC Public Health 2011, 11:281 http://www.biomedcentral.com/1471-2458/11/281 [10]. Meanwhile, there are few studies assessing WTP for valuing someone else’s health state (e.g. parental WTP) [8,9,17,18]. The objective of this paper was to assess parental will- ingness to pay for child car safety seats in Mashad, Iran. Methods This cross-sectional study was conducted in Mashad in July to October 2009. Mashad is the second largest city in Iran with a population of about 3 million at the time of study [19]. In Mashad, the death rate of RTCs is high (46.4 per 100,000 population including all age groups [4]). Participants were parents of kindergarten children who owned personal automobiles and were willing to participate in the study. We aimed for a sample of 590 parents considering a 1.5 design effect. In the pilot, 49 percent of parents were willing to pay the amount of money which was nearly adequate for buying a CSS in Iran (100$ or above). Multistage cluster sampling was used for selecting participants in which Mashad districts served us as strata and kindergartens as clusters. From each of 10 municipality districts of Mashad, 5 kindergar- tens were selected randomly for data collection (50 kin- dergartens in total). From each kindergarten, all parents who met the inclusion criteria (parents of children aged less than five years, who owned cars) were invited to participate in the survey. For each child we interviewed only one parent, as no significant differences were observed between the reported WTP by the mother and father of each child in the pilot study. Interviews were performed in selected kindergartens using an interviewer-based questionnaire. The question- naire included demographic data, parent’s perceived effi- cacy of child safety seat and whether the parent had previously received any advice on using the safety seats. Past history of RTCs in the family was also recorded. Then, the parents were provided with pictorial introduc- tion of the main types of safety seats which are recom- mendable according to the child’s age. It included the presentation of a safety seat scenario including informa- tion on child car passenger deaths in Iran and available evidence on efficacy of safety seats. Then they were asked to choose from the available options the maxi- mum amount of money they were willing to pay for having a seat. Contingent valuation was used with multi- ple choice questions for assessing WTP among parents. These options ranged from zero to $300 in seven choices that were developed based on the pilot study. The median and mean amount of money the subjects were willing to pay was estimated, and the relationships with the parents’ and children’s characteristics were assessed. Kruskal-Wallis and Mann-Whitney U tests were employed to study the WTP value according to Characteristic Child Age groups (months) Sex Mother’s level of education Father’s level of education Household income group Page 2 of 6 the study variables using SPSS software for Windows 15.0. WTP was also transformed into a dichotomous categorical variable. This variable was coded zero for WTP less than the minimum amount of money enough to obtain a CSS in Iran(<$100) and 1 for WTP enough to buy a CSS(≥$100). Logistic regression was used to develop the econometric method. A P value less than 0.05 was considered statistically significant. Ethical Approval The proposal of this research was approved by the ethi- cal committee of Sina Trauma Research Center affiliated to Tehran University of Medical Sciences. Our research conformed to the Helsinki Declaration and local legisla- tions on Ethical Principles for Medical Research Invol- ving Human Subjects. Each potential subject (parent) was adequately informed of the aims, methods, sources of funding, institutional affiliations of the researchers and the anticipated benefits of this research for the society. He/She was also informed of the right to refuse to participate in the study. The interview was performed after ensuring that the parent has understood the infor- mation and is willing to participate. Results A total of 590 parents who met the inclusion criteria and were willing to participate in the study were included. The included parents reported the mean age of their children to be 33.5 months (SD = 16). Demo- graphic characteristics of the responders and their chil- dren appear in Table 1. Table 1 Demographic characteristics of study participants Number Percent 0-11 12-23 24-35 36-47 48-59 female male (university education) (university education) Low income High income Total Moderate income $500-$1000 195 (33) 69 126 98 163 134 303 287 286 312 <$500 >$1000 Didn’t answer 590 11.7 21.6 16.6 27.6 22.7 51 49 49 53 282 (47.5) 53 (9.5) 60 (10) 100