Emergency ambulance system in Japan
In Japan, local governments organize emergency ambulance service as a public service. Anyone can use an ambulance free of charge by making a phone call to "119". Ambulance crews are dispatched for all emergency calls, and all patients attended by a crew are transported to a hospital unless they refuse. Most local governments staff ambulances with emergency life-saving technicians who are trained for cardiopulmonary resuscitation [15, 25, 26].
Study site and study design
The study was conducted in Yokohama, Japan, which has a population of 3,579,133 (2005 census) and covers an area of 434 square kilometers. In Yokohama, the number of ambulances dispatched in 2005 was 1.58 times greater than that in 1995 , although the population in 2005 was only 1.08 times greater than that in 1995 . The city's ambulance transport service is unified and managed by the Emergency Medical Division of the Yokohama Fire Bureau.
We conducted an anonymous self-administered questionnaire-based survey targeting 3,600 city residents randomly selected from the city resident registration list; 1,200 city residents were extracted from each of three age groups, 20–39 years, 40–64 years, and 65 years or over. Questionnaires were distributed once and returned in September 2004. Reminders were not sent. Detailed information about sampling for the study has been published elsewhere .
The questionnaire consisted of three parts. The first part included questions on demographic and socioeconomic characteristics such as the respondent's age, gender, and pretax annual household income.
The second part included hypothetical questions pertaining to ambulance use. We applied the dichotomous choice method to estimate the probability of calling an ambulance [29–31]. Three hypothetical nonemergency situations were presented. Scenario 1 represented a situation in which the respondent faces a nonserious condition such as an ankle sprain or bruise on the leg. Scenario 2 represented a situation in which the respondent's child or young relative faces a nonserious condition such as a nose cold. Scenario 3 represented a situation in which the respondent's elderly relative faces a nonserious situation such as lack of transport to a clinic. The influence of user charges was assessed along with the hypothetical questions by presentation of one of eight possible prices ($0, $9.50, $28.50, $47.50, $95.00, $190.00, $285.00, and $475.00; $1 = ¥105) for use of an ambulance. Each respondent was shown only one price randomly selected from the eight prices for each of the three hypothetical scenarios. For each situation, respondents answered "yes" if they would call an ambulance or "no" if they would not. The three hypothetical scenarios were as follows:
Scenario 1: At around 6 a.m., you miss your step and tumble down the stairs. You then develop pain in your legs, but you can walk with difficulty. If you were in this situation, would you call an ambulance?
Scenario 2: One morning, a child who is living with you develops a cough and nasal discharge. You give him/her a drug, which has been kept at home for future use, but the symptoms do not disappear even by 8 p.m. on the same day. If you were in this situation, would you call an ambulance? Even if you do not live with a child, please answer the question as if you do.
Scenario 3: It's around 8 a.m. An elderly person who is living with you needs to go to the hospital to see his/her primary care physician. Normally, someone in your family would drive the elderly person to the hospital, but no one can do so today. If you were in this situation, would you call an ambulance? Even if you do not live with an elderly person, please answer the question as if you do.
The third part included questions on the city's emergency medical system, such as "Have you ever used an ambulance?" "Do you feel hesitant to call an ambulance?" "Are you familiar with the primary emergency medical centers?" "Are you familiar with the emergency medical information center?" and "Do you know of any private patient transport service?"
Analysis of the influence of socioeconomic factors
The probability P of a "yes" response to the dichotomous choice questions was expressed by a probit model [32, 33]:
where "Y" equals 1 if the respondent chose "yes" and 0 if otherwise. Φ is the standard cumulative normal distribution, and βn is the estimated parameter vector. Price is the hypothetical price of ambulance use and is treated as a quantitative variable. Gender is a dummy variable (male = 1, female = 0). Age is the age group that the respondent belongs to, with 1 representing 20–29 years, 2 representing 30–39 years, 3 representing 40–49 years, 4 representing 50–59 years, 5 representing 60–69 years, 6 representing 70–79 years, and 7 representing 80 years and over. Family is a dummy variable for family structure: living alone was expressed as 1 (other = 0), when the response to Scenario 1 was analyzed; living with children aged 5 years or younger was expressed as 1 (other = 0) when the response to Scenario 2 was analyzed; living with a relative aged 65 years or older was expressed as 1 (other = 0) when the response to Scenario 3 was analyzed. Income is the pretax annual household income, expressed as 1 if less than $19,000, 2 if $19,000 to $37,999, 3 if $38,000 to $56,999, 4 if $57,000 to $75,999, 5 if $76,000 to $94,999, and 6 if $95,000 or more. Car is a dummy variable for possession of a car by which the respondent could visit a hospital or clinic (yes = 1, no = 0). History is a dummy variable for the respondent's past ambulance use (yes = 1, no = 0). Hesitation is a dummy variable for feeling hesitant to use an ambulance (yes = 1, no = 0). E.Center is a dummy variable for knowledge of a primary emergency medical center (yes = 1, no = 0). E.Info is a dummy variable for knowledge of the emergency medical information center, which serves as a directory where individuals can obtain the name of a suitable hospital or clinic (yes = 1, no = 0). P.Trans is a dummy variable for knowledge of a private patient transport service (yes = 1, no = 0).
The marginal effect of each factor, that is, a change in the probability of a "yes" response (for an independent binary variable) or of a one-unit increase (for an independent ordinal variable), i.e. estimated percentage of incremental demands for ambulance use produced by socioeconomic factors, was also computed with the probit model.
STATA/SE 8.2 software for Windows (Stata Corp., College Station, Texas, USA) was used for all statistical analyses including probit regression analysis. P values of less than 0.05 were considered statistically significant.
The questionnaire-based study was conducted anonymously. No personal information, such as the respondent's name or address, was contained in the returned questionnaires. Analysis of ambulance calls to the Yokohama Fire Bureau to estimate incremental demand was also conducted anonymously. The study was approved by the Committee on the Regional Emergency Medical Service System of Yokohama after ethical aspects of the study were reviewed by the Human Rights Affairs Division, Civic Affairs Bureau, City of Yokohama.