The Japan Dental Association was established in 1903. Its membership excluding corporate members was 64,990 dentists in 2012, covering about 66% of dentists working in hospitals or clinics in Japan. About 85% of the dental clinics that are members of the Japan Dental Association are private and the rest are corporate. The authors used the data on private dental clinics in October, with a sampling rate of 0.10 in the articles [5], [6] and [7]. Table selleckchem 1 shows basic statistics on income and expenses of private dental clinics in Japan, including a detailed breakdown [5].

The mean age of the owner was 53.6 years. The mean number of patients per day was 20.1 people with a minimum of 0.42 people and maximum of 87.3 people. Net income in October, 2006 ranged from −1,069,460 to 7,218,012 yen, and the mean, median and standard deviation of net income were 1,252,605, 1,072,101, and 900,765 yen, respectively. Fig. 4 shows histograms of the net income of private dental clinics in October, 1996 and October, 2006 [6]. In 1996, the histogram was similar to a normal distribution, but, in 2006, the distribution was positively skewed, with the mean dragged to the right by a few high scores. The distribution between dental clinics with a low net income and those with a high net income widened from 1996 to 2006, as seen by the increase in size of the coefficient of variation, calculated

by dividing standard deviation with mean, from 65.7% in 1996 to 71.9% in 2006. The Central Social Insurance Medical Council always uses means MK-8776 in vivo as a measure of central tendency of net income. However, because the

distribution in 2006 was not normally distributed, the median (1,072,101 yen) may be more appropriate than the mean (1,252,605 yen) as a measure of central tendency of net income. It is noteworthy that by using the mean as a measure of central tendency in 2006, net income was over-estimated by about 17%. This over-estimation could reduce dental treatment fees in public health insurance at the meeting of the Florfenicol Central Social Insurance Medical Council, and could result in reduction of the net income of dental clinics in Japan. It is also important to note that the data used by the Central Social Insurance Medical Council was based on the month of June. June usually has the largest number of patients because dental examinations in schools (and some companies) are conducted from April to June every year. The data used by the Central Social Insurance Medical Council is therefore an over-estimate, and the use of the data on only June may inappropriately affect management of dental clinics in Japan. Table 2 shows factors relating to whether or not the net income of private dental clinics exceeds the median in 1996 and 2006 using multiple logistic regression models. The dependent variable in the model takes the value of 1 if the net income is more than median and 0 if the net income is equal or less than median.