A survey was conducted on WTP for medical services, based on a questionnaire survey using the Internet. The population was assumed to be general public between 40 and 59 years old residing in Japan. For the survey, cooperation was obtained from an Internet research company located in Tokyo, with approximately 195,000 Internet users registered as monitors. 2,500 were randomly selected from the registered men and women between 40 and 59 years old (approximately 52,200 people). Emails requesting cooperation in the questionnaire survey were sent all at once at 19:00, February 22, 2005. Individuals subject to the survey were able to respond and reply to the questionnaire voluntarily and anonymously by accessing the website where the questionnaire survey was conducted, and by entering the answers directly on the survey form on the web.
This research is simply based on the anonymous self-administered questionnaire without experimental interventions. From the cover letter of the questionnaire, the subjects were well informed that 1) data collection and analysis was fully anonymous so that their private information would be completely protected, 2) all the answers would be kept confidential, processed statistically, and used only for scientific study, and 3) they could either participate of their own accord or refuse to participate.
We aimed at collecting 700 to 800 samples. Since the sample size was not based upon any pre hoc power calculations, this was a sample of convenience. Each time after e-mail transmission, the number of response was checked. 795 responses were collected in only 48 hours. At that point, we immediately closed down the website and terminated the survey. The response rate was calculated as 31.8% (= 795/2500). All questions in the survey form were multiple-choice questions, and the form was configured in a way that made it impossible to move on to the next question if a question was left unanswered. This made it possible to acquire completely valid responses with no missing data in all samples, and inevitably resulted in a valid response rate of 100%.
Hypothetical scenarios for asking WTP for medical services
Acute illnesses with subjective symptoms were first divided into the following three categories:
Category 1: There is no risk of death or disability.
Category 2: There is no risk of death, but there is a risk of serious disability.
Category 3: There is a risk of death.
Common cold (CC), retinal detachment (RD) and acute myocardiac infarction (MI) were chosen as illnesses that fall into Categories 1, 2 and 3, respectively. Hypothetical scenarios relating to these three illnesses were presented, and the WTP for medical services was asked. This made it possible to estimate the respective prices of individual medical services deemed reasonable by general public, with given assumptions on symptoms and conditions. Individuals subject to the survey were required to select one of the prices from among the seven options presented in each question, based on "payment cards" [11–13]. The hypothetical scenarios and the options presented were as follows.
Category 1 (Common Cold, CC)
Question: "Suppose you have a temperature of 38.5 degrees Celsius, feel lethargic from head to toe and visit a medical institution as an outpatient. You are diagnosed with a common cold, and are prescribed oral medicine. What is the maximum price you are willing to pay for the medical services provided?"
Options: $10, $20, $30, $40, $50, $100, and $200
Category 2 (Retinal Detachment, RD)
Question: "Suppose you are at risk of losing sight in one of your eyes because your left eye suddenly suffers retinal detachment. As a result of surgery performed on your left eye and twelve days of hospitalization, you avoid becoming blind. What is the maximum price you are willing to pay for the medical services provided?"
Options: $1,000, $1,500, $2,000, $2,500, $5,000, $10,000, and $20,000
Category 3 (Myocardiac Infarction, MI)
Question: Suppose your life is at risk as you suddenly suffer acute myocardiac infarction, and you are taken to hospital by ambulance without regaining consciousness. You escape death as a result of receiving cardiopulmonary resuscitation and undergoing emergency percutaneous coronary intervention. After two months of hospital treatment, you more or less restore your health and are discharged from hospital. What is the maximum price you are willing to pay for the medical services provided?"
Options: $3,000, $6,000, $9,000, $15,000, $30,000, $60,000, and $120,000
Basic attributes of individuals subject to survey
The survey included questions on factors deemed to affect WTP such as age, sex, annual household income, private health insurance policy holding status, hospitalization history, and subjective fitness level.
In the question on private health insurance policy holding status, three options were given: "Have insurance", "Don't have insurance", and "Don't want to answer". As Japan implements a national health insurance plan, almost all Japanese citizens can reap the benefits of public health insurance. If a patient receives medical services based on public health insurance, he/she must incur co-payments accounting for a certain percentage of the expenses. Such percentage is prescribed by law (such as the Health Insurance Law), uniformly at 30%, for all standard medical services covered by insurance, excluding elderly persons and children. To prepare for the 30% co-payment burden, many Japanese people buy private medical insurance services sold by private insurance companies. However, the actual number of buyers of such services across Japan is unknown.
As for the subjective fitness levels, the individuals were asked to describe their current status on five levels: "Very good", "Good", "Average", "Slightly bad" and "Bad".
Compilation of WTP data
Mean WTP and median WTP were calculated with respect to each scenario. Variable X denoted each presented price, while the number of individuals who are willing to pay more than the presented price (i.e., individuals who can tolerate that price) denoted the number of tolerant individuals (Y). The values were plotted on an X-Y plane and approximated on the basis of the following exponential function.
Y = αeβX(*)
X: Price, Y: Number of tolerant individuals, α, β: Constants
Constants α, β in the formula above (*) and the coefficient of determination adjusted for the degrees of freedom R2 were calculated.
WTP by annual income
The relationship between an individual's WTP and his/her income was studied.
Firstly, the sample group was divided into three groups: low-income group with an annual income less than 40,000 US dollars (92 individuals), medium-income group with an annual income of 40,000 US dollars or more but less than 80,000 US dollars (371 individuals), and a high-income group with an annual income of 80,000 US dollars or more (266 individuals). In total, 729 individuals were subject to analysis, excluding 66 individuals who responded "Don't want to answer" the question on annual income. With respect to each scenario and group, presented prices was plotted on the horizontal axis, while the ratio of individuals who can tolerate purchasing the medical services at a higher price than the presented price was plotted on the vertical axis. This made it possible to visually represent how WTP varied with the income level.
Next, the mean WTP was compared among the three groups (low-income, medium-income and high-income groups) in each scenario. Due to doubts about the normality and homogeneity of variance regarding the distribution of WTP, a Kruskal Wallis test (nonparametric test) was adopted.
Further, in order to adjust various factors at the same time, regression analysis was conducted assuming that WTP is a dependent variable and that annual income, age, sex, private health insurance policy holding status, hospitalization history, and subjective fitness level are independent variables. Taking into account that the dependent variable is ordinal data, ordinal regression analysis was adopted rather than normal multiple regression analysis. Pseudo-r squares were calculated for the ordinal regression models .
P values of less than 0.05 were considered to be statistically significant. All statistical analyses were performed using statistics software SPSS ver.13.0 (SPSS Ltd., Chicago, USA). The exchange rate is assumed to be 105 yen for the U.S. dollar.