Estimation of the Future Numbers of Patients with Mental Disorders in Japan Based on the Results of National Patient Surveys

To estimate the future numbers of patients with mental disorders, schizophrenic disorders, and neurotic disorders, prevalence obtained from the National Patient Surveys conducted by the Ministry of Health and Welfare of the Japanese government was projected by using linear models by age and sex. The prevalence of whole mental disorders and neurotic disorders will increase, while that of schizophrenic disorders will not do so much. The numbers of patients with mental disorders were estimated to be 973 thousand for males and 1,359 thousands for females in the year of 2008, which were 622 thousand and 733 thousand in 1993, respectively. The diseasespecific numbers in 2008 were 562 thousand for schizophrenic disorders and 867 thousand for neurotic disorders, both were 451 and 437 thousand in 1993, respectively. Because of the increase of old age population, the number of old patients with each disorder will also become large. J Epidemiol, 1997; 7 : 214-220.

Yosikazu Nakamura, Toshiyuki Ojima, Izumi Oki, Shinichi Tanihara and Hiroshi Yanagawa To estimate the future numbers of patients with mental disorders, schizophrenic disorders, and neurotic disorders, prevalence obtained from the National Patient Surveys conducted by the Ministry of Health and Welfare of the Japanese government was projected by using linear models by age and sex.The prevalence of whole mental disorders and neurotic disorders will increase, while that of schizophrenic disorders will not do so much.The numbers of patients with mental disorders were estimated to be 973 thousand for males and 1,359 thousands for females in the year of 2008, which were 622 thousand and 733 thousand in 1993, respectively.The diseasespecific numbers in 2008 were 562 thousand for schizophrenic disorders and 867 thousand for neurotic disorders, both were 451 and 437 thousand in 1993, respectively.
Because of the increase of old age population, the number of old patients with each disorder will also become large.
Epidemiologic data are essential to take efficient measures for a disease.To clarify the frequency of the disease, such as incidence rates, prevalence, and mortality rates, is important, and health administrations should be based on the data.The future estimation of the data is meaningful to discuss the planning of medical supplies in the future as well as considering the future directions of epidemiologic studies.
Fujita has estimated the number of patients with mental disorders using the National Patient Surveys conducted by the Ministry of Health and Welfare1,2) In these papers he has pointed out the increase of the number, in particular among out-patients.
We projected the prevalence and the number of patients with mental disorders using the total numbers of patients obtained from the National Patient Surveys and estimated the future figures.

MATERIALS AND METHODS
The target diseases in the study are three; mental disorders, of which the code number of the Ninth Revision of International Classification of Diseases (ICD-9th) is 290-319, schizophrenic disorders (secondary mention, ICD-9th:295), and neurotic disorders (secondary mention, ICD-9th: 300).Data of National Patient Surveys conducted by the Ministry of Health and Welfare of the Japanese government since 1984, when the current survey methods started, were used.
The total numbers of patients with such diseases, including even out-patients that did not visit hospitals nor clinics on the survey day, were obtained by age and sex.The data in 1984, 1987, and 1990 were from the results of special calculation conducted for specific research committee, 4 and those in 1993 were from a CD-ROM provided by the Ministry.
The total number of patients was calculated by the following formula; The number of patients = inpatients on the survey day + first-visiting out-patients on the survey day + re-visiting out-patients on the survey day x average interval from the last visiting x correcting index (6/7).First, we obtained prevalence of the diseases, the total numbers of patients divided by population, by age and sex.Next, a linear regression model was estimated, of which the independent variables were calendar years, and the dependent ones were prevalence, for each age and sex group.Future preva-Received January 8, 1997; accepted May 14, 1997.Department of Public Health, Jichi Medical School, Tochigi, Japan.Address for correspondence : Yosikazu Nakamura,Department of Public Health, Jichi Medical School, 3311-1 Yakushiji Minamikawachi, Tochigi 329-0498, Japan lence were estimated with the linear model.Finally, the total number of patients in the future was calculated by multiplying the estimated prevalence and the future population reported by the Ministry of Health and Welfare.4) The sum of the numbers of patients in all age classes was the grand total number of the patients in each sex and disease.
Because the data used in the study were in 1984, 1987, 1990, and 1993, we estimated the numbers in every three years starting in 1996.The final year for the estimation was 2008.

RESULTS
The prevalence of three disorders were shown in Tables 1,  2, and 3.In the tables, numerals from 1984 through 1993 were the results from the National Patient Surveys, and those from 1996 through 2008 were the results of the estimation due to the current study.The prevalence of mental disorders was estimated to increase among every age and sex class (Table 1).The prevalence among all age groups would be 1.5 through 2 times as large as that at present.The changes of prevalence of schizophrenic disorders depended on the age; it was estimated to decrease or stay in the same levels among young age groups less than 45 years, but increase among old age groups (Table 2).The prevalence of neurotic disorders was estimated to elevate among both males and females (Table 3).The numbers of patients with the three disorders, prevalence multiplied by populations, are shown in Tables 4, 5, and 6.For the whole mental disorders (Table 4), the numbers among young age groups would not increase, while those among old age peoples were estimated to elevate.The numbers of patients with schizophrenic disorders aged less than 55 years would decrease or stay at the same level (Table 5).On the other hand, the numbers among old age groups would expand.The patients with neurotic disorders increase in all age groups except for 0-4 years (Table 6).Figures 1 and 2 show the total numbers of patients in all age groups, respectively.The numbers of patients with mental disorders would be about one million among males, 1.4 million among females in 2008.Those with schizophrenic disorders would be approximately 300 thousand among both males and females, and those with neurotic disorders were estimated to be 300 thousand among males and 500 thousand among females in 2008.

DISCUSSION
Prevalence and the number of patients with a disease are essential for epidemiologic studies as well as health administration.Several Japanese studies provide us these data of mental disorders, but many of them are conducted in specific areas or fields.5-8) While researchers stress the importance to reveal the morbidity, the data are limited.1,2,,9,10) In this study we observed the prevalence of mental disorders and future projection figures for whole Japan.
To date we have shown two results for other diseases using same data and methods.11-12)The advantages and disadvantages of the methods are discussed in these papers.Because the methods are appropriate with the limited current data, we have concluded that the results we provide is useful although it is not the best method.
We had better stress two other limitations of the study design; weakness on robustness of the models, and birth-cohort effect.Both of them are from the small number of data observed, which consist of those for 4 years.In particular, our estimation was extrapolation so that the results would be affected by some outlyers.The birth-cohort effects might exist among those with mental disorders, because social factors should affect the mental status.We would consider these points when the data will be obtained year by year.
The current results tell us that the number of patients with mental disorders will increase, in particular for those who are less than 5 years of age and are more than 50.Nevertheless, the diseases consisting of the disorders are expected to change; the schizophrenic disorders decrease among young age groups but increase among old age groups, while the neurotic disorders are estimated to increase in almost all age groups.
Three factors influence the prevalence and the number of patients with a disease; the incidence rate, the time duration from the disease onset through the end of the disease, and the reduction rates from the disease group that comprise mortality rate and rate of cure.We guess that the reduction of prevalence of schizophrenic disorders among the youth will be the results of the decrease of incidence.13)Onthe other hand, the expanding of prevalence and the number with schizophrenic disorders among the old will be caused by the elongation of the time duration ,14)which may be due to the decrease of mortality rate.A few studies observed the mortality among patients with mental disorders,15-17) but the chronological trends are still unclear.The incidence rate of schizophrenia is not so high among old age groups 9) that it is reasonable to explain the phenomenon that patients with the disease affected when they were young become likely not to die because of the improvement of management of not only the disease but also other disorders influencing the mortality, such as cardiovascular diseases and cancers.
The increase of the neurotic disorders may be due to two factors; the true increase of the prevalence of the disease among the population and the improvement of the accessibility to visit hospitals and clinics.Because the current results are based on the National Patient Surveys, which comprise data of patients visiting hospitals and clinics, our estimations are for those who visit the medical affiliations as well.Therefore, we cannot discuss the true chronological changes of the prevalence.The number of clinics without beds for mental disorders are increasing, especially in urban areas in Japan, 18,19) and this must affect the number of patients visiting clinics with neurotic disorders.In other words, easy accessibility to such clinics have patients with so mild disorder that they would not visit hospitals go to the medical facilities.
It is well known that in Japan medical supplies induce patients.This means that the number of patients depends on the numbers of hospitals and clinics, physicians, and beds.A nationwide survey tells us that one third of inpatients with mental disorders who had stayed on hospitals for more than 2 years could discharge with social facilities.20)If the political decisions would change these numbers in the future, the current results would be incorrect.Our data are based on the hypothesis that the current medical supply conditions will keep on in the future.
In conclusion, we have shown the future projection of prevalence and the numbers of patients with mental disorders.The numbers increase 1.5 to 2 times larger that current status, but the condition that consists of the whole mental disorders will change.
Estimation of the Future Numbers of Patients with Mental Disorders in Japan Based on the Results of National Patient Surveys.

Fig 1 .
Fig 1. Secular trends of the total numbers of patients with mental disorders (ICD 9th; 290-319) by sex.

Figures
Figures between 1984 and 1993 are from the results of National Patient Surverys conducted by the Ministry of Health and Welfare of the Japanese government, and those between 1996 and 2008 are the estimated numbers

Figures
Figures between 1984 and 1993 are from the results of National Patient Surverys conducted by th e Ministry of Health and Welfare of the Japanese government, and those between 1996 and 2008 are the estimated numbers

Table 2 .
Prevalence of schizophrenic disorders (ICD 9th : 295, per 1000 population) in Japan , 1984-2008, by age and sex.Figures between 1984 and 1993 are from the results of National Patient Surverys conducted by the Ministry of Health and Welfare of the Japanese government, and those between 1996 and 2008 are the estimated numbers

Table 4 .
Number of patients with mental disorders (ICD 9th : 290-319, in thousand) in Japan, 1984-2008, by age and sex.Figures between 1984 and 1993 are from the results of National Patient Surverys conducted by the Ministry of Health and Welfare of the Japanese government, and those between 1996 and 2008 are the estimated numbers using prevalence shown Table1.

Table 5 .
Number of patients with schizophrenic disorders (ICD 9th : 295, in thousand) in Japan, 1984-2008, by age and sex.
Figures between 1984 and 1993 are from the results of National Patient Surverys conducted by the Ministry of Health and Welfare of the Japanese government, and those between 1996 and 2008 are the estimated numbers using the prevalence shown Table2.

Table 6 .
Number of patients with neurotic disorders (ICD 9th : 300, in thousand) in Japan, 1984-2008, by age and sex.Figures between 1984 and 1993 are from the results of National Patient Surverys conducted by th e Ministry of Health and Welfare of the Japanese government, and those between 1996 and 2008 are the estimated numbers using prevalence shown Table3.
shows ratios of the numbers estimated in 2008 and observed in 1993 by age, sex and disorder.For mental disorders, the increase would be prominent among the youngest age group and old age ones.The numbers of patients with schizophrenic disorders would increase among old age groups but not among young adults less than 55 years of age.Neurotic disorders would be more prevalent among all age groups.