ORIGINAL ARTICLE
Comparing medical expenditures of smokers and nonsmokers
in studies using direct methodology in Japan
Naoki Shimada1, Michiko Miyakawa2, Masayuki Tatemichi3, Yumi Otahara4, Takashi Izuno,4and Minoru Sugita4

Department of Preventive Medicine and Public Health, School of Medicine, Keio University, Tokyo, Japan
2
Faculty of Humanity and Environment, Hosei University, Tokyo, Japan3
Department of Hygiene and Preventive Medicine, Showa University School of Medicine, Tokyo, Japan
4
Department of Environmental and Occupational Health, Toho University School of Medicine, Tokyo, Japan
1(Received for publication on February 16, 2007)(Revised for publication on March 29, 2007)(Accepted for publication on April 19, 2007)

Abstract. Numerous epidemiologic studies have revealed that smoking is a significant risk
factor of many diseases. Some studies reported increase in medical expenditure by smoking using odds or hazard ratios between smoking and diseases in epidemiologic studies.
The purpose of the present study is to investigate the ratios of mean medical expenditures
between smokers and nonsmokers from studies conducted observing medical expenditure
directly in Japan. We collected 11 published articles of studies conducted observing medical
expenditures of smokers and nonsmokers directly in Japan. The weighted geometric meanof ratios between age-adjusted mean medical expenditures for smokers and nonsmokers of
National Health Insurance and Government-Managed Health Insurance beneficiaries which
included many elderly individuals was somewhat greater than 1.0, while the value of Society-Managed Health Insurance that included a small number of elderly people was less than
1.0. Smoking and smokers’ indifference to health increase the medical expenditure of thesmokers, especially elderly smokers. It was not determined, however, whether the mean
medical expenditure of smokers is actually greater than that of nonsmokers. (Keio J Med 56(2) : 53 － 60, June 2007)
Key words: medical expenditure, smoker, nonsmoker, directly observed studies, Japan
Nonstandard abbreviations used in this paper:
NHI: National Health Insurance
GMHI: Government-Managed Health Insurance
SMHI: Society-Managed Health Insurance

Introduction

creases in medical expenditures for smokers calculated
indirectly from odds or hazard ratios between smoking
and the incidence and/or mortality rates cited from epidemiologic studies. The odds or hazard ratios are muchgreater than 1.0. Let those studies using odds or hazard
ratios be indicated as “studies using indirect method.” Inother studies,1 6 -2 9 the medical expenditures of smokers
and nonsmokers were directly observed and the marginalincreases in medical expenditures by smoking were cal-Numerous epidemiologic studies have reported thatsmoking causes many diseases, such as cancer, cardiovascular diseases, respiratory diseases, and others. Increases in incidence and mortality rates of these diseases
by smoking have been detected in the studies and described in many textbooks.
There are many studies1- 1 5 indicating marginal in-

To whom correspondence should be addressed: Minoru Sugita, M.D., Ph.D., Department of Environmental and Occupational Health, Toho University Schoolof Medicine, 5-21-16 Omori-nishi, Ota-ku, Tokyo 143-8540, Japan, E-mail: sugita@med.toho-u.ac.jp
53

Shimada N, et al: Medical expenditure of smokers

54

culated. Let those studies conducted by direct observation be indicated as “studies using direct method.” Somestudies using the direct method reported that medical expenditures of smokers were less than those of nonsmokers while others reported that they were greater.
Mortality, incidence, and prevalence rates of lifestylerelated diseases and population medical expenditures are
increasing rapidly3 0, 3 1 due to the rapid aging of society
in Japan.32 Smoking-related diseases are typical among
lifestyle-related diseases. The national and local governments in Japan are in financial difficulties. Therefore,studies in which the influence of smoking on medical expenditures is investigated are necessary and very important given the recent socioeconomic condition in Japan
from the viewpoint of public health.
The purpose of the present study is to compare medical
expenditures of smokers and nonsmokers from studies
using the direct method conducted in Japan.
Materials and Methods
Articles and information collected
We collected 12 published articles of studies conducted
observing medical expenditures directly in Japan using“PubMed” and “Japana Centra Reuo Medicina WEB”
regarding medical expenditure, medical cost, smoking,and/or smoker, and using requotations from articles on
studies by direct and indirect methods found previously.
If two or more articles were published on the same study,
the most recent article was selected and the earlier
article(s) not used. Eleven articles19 -29 were selected for
calculating the ratio of mean medical expenditure between smokers and nonsmokers. We did not find many
articles in which medical expenditures of female smokers were described. Thus, in principle, the medical expenditure ratio investigated in the present study was between male smokers and nonsmokers.
The following information was needed for the present
study: (1) age-adjusted mean medical expenditures ofsmokers and nonsmokers, (2) numbers of subjects ofsmokers and nonsmokers by age category, (3) ages ofsmokers and nonsmokers, (4) the type of medical careinsurance, and (5) the year of submission of health insurance claims. When the age-adjusted mean medical expenditures by smoking status were described in articles,2 0, 2 6, 2 7 they were employed in the present study.
When (i) the age-adjusted medical expenditures bysmoking status were not given and (ii) the mean medical
expenditures and numbers of subjects according to age
category and smoking status were given,19, 21-25 the ageadjusted mean medical expenditures were calculated bya direct method using (ii), i.e., the mean medical expenditures and numbers of subjects by smoking status andage category and numbers of total subjects for all smok-

ing status groups by age category. When (i) and (ii)were not described in articles,28, 29 we asked the authorsof the articles to provide information on (ii), and the ageadjusted mean medical expenditures were calculated bya direct method using the information provided by theauthors. The age-adjusted medical expenditure ratio between smokers and nonsmokers was obtained from theage-adjusted mean medical expenditures of smokers andnonsmokers. When the numbers of smokers and nonsmokers were not indicated in an article,2 1 the numbers
were calculated from the number of male subjects andmale smoking rate. When the mean age of subjects was
not given in an article, 1 9- 2 1, 2 3, 2 4, 2 7, 2 8 the mean ages
were obtained from the numbers of subjects and the center ages according to age category. The mean year ofsubmission of health insurance claims was calculated
from the year of submission and the number of subjects
in the 11 studies as a weighted mean.
The health insurance system in Japan is composed oftwo systems. The first is for employees and their dependents, the second is a community-based health insurance
system mainly used by farmers, the self-employed, pensioners, and their dependents. The second system iscalled the National Health Insurance (NHI). The firstcontains Government-Managed Health Insurance(GMHI), Society-Managed Health Insurance (SMHI),
and Seamen’s Insurance, which is very small.3 3 SMHI
beneficiaries are employees of large corporations and thenational and local governments and teachers of private
schools before retirement and their dependents. GMHI
beneficiaries are employees of small and medium size
enterprises and their dependents. NHI and GMHI beneficiaries include many elderly individuals while SMHI
beneficiaries do not.
When the age-adjusted mean medical expenditures ofsmokers were not described in articles,1 9, 2 2-2 5, 2 8, 2 9 thevalues were calculated from the age-adjusted mean medical expenditures of current and former smokers using thenumbers of total subjects for all age groups of current
and former smokers in the articles as the weighted
means, i.e., direct adjustment.
Medical expenditure in the present study is calculated
from the amounts of health insurance claims. Therefore,
medical expenditure in the present study does not containindirect costs.
Geometric mean of ratios
Weighted geometric mean of ratios between age-adjusted mean medical expenditures of smokers and nonsmokers was calculated. The weight of the i-th study is
wi = √1 / (1/nSi + 1/nNi),
where nS and nN are numbers of subjects of smokers andnonsmokers. Variance of natural logarithm of ratio isKeio J Med 2007; 56 (2): 53－ 60

55

Table 1 Year of Publication, Type of Health Insurance, Age of Subjects, Calendar Year of Submission of Health Insurance Claims, Duration ofSubmission of the Claims, Numbers of Smokers and Nonsmokers, the Age-adjusted Ratio of Mean Medical Expenditure between Smokers andNonsmokers, and Annual per Capita Medical Expenditure of Nonsmokers for each Article
Reference Published Health Age (years)
Submission
Number of subjects Medical expenditure ratio Annual per capita medical
number year
insurance Range Mean Year
Duration Smokers Nonsmokers
expenditure for nonsmoker (¥)
19
1987
NHI
30-70+ 54.4ｔ 1983
12months 1,343
211
1.118
105,351
20ｅ
1989
SMHI
20-60+ 44.2ｔ 1985-86 12months
484
468
0.909
77,20021
1992
NHI30-69 60.6ｔ 1990-91 12months 1,601ｐ
400ｐ
0.735
452,759
22
1993
SMHI
18-79 37.9 1986-90 48months 8,825
3,489
0.888
155,100
23ｉ
1994
NHI
30-80+ 57.6ｔ 1989-90 12months
770
141
1.017
268,510
24
1996
SMHI
40-73 51.5ｔ 1989
12months 4,093
702
0.741
191,123
25
1996
SMHI
30-75 41.5 1990
12months 1,022
359
0.728
47,41326ｅｘ，ｆ 2000
NHI
60-84 60+ 1998
1month 1,585
528
1.088
27
2001
NHI
40-79 60.0ｔ 1995-97 30months 18,825
4,256
1.111
330,480ｉ
28
2003
GMHI 26-86 50.7ｔ 1998-99 12months 2,621
659
1.219
2,987
29ｄ
2003
SMHI
18-76 39.5 1996-98 36months 66,641
29,6580.951
66,663Abbreviations: d: dental expenditure excluded, e: former smokers included among nonsmokers,
ex: former smokers excluded, f: females included and sex-adjusted,
GMHI: Government-Managed Health Insurance, i: inpatients excluded,
NHI: National Health Insurance, p: proportional distribution by smoking rate,
SMHI: Society-Managed Health Insurance, t: calculation from tables$1 = ¥80 - 105 (in 1995)

obtained as sum of reciprocal numbers of samples ingroups. Confidence interval of the weighted geometricmean of the ratios is not calculated in the present study,
because the information on scale parameter of the medical expenditures is not obtained.
Results
Table 1 shows the reference number, year of publication, type of health insurance, age of subjects (range andmean), calendar year of submission of health insurance
claim, duration of the submission of the claims, numbersof subjects of smokers and nonsmokers, the age-adjusted
mean medical expenditure ratio between smokers andnonsmokers, and annual per capita medical expenditureof nonsmokers in each of the 11 articles. The articles arearranged in the order of year of publication in Table 1.
The weighted geometric mean of ratios between ageadjusted mean medical expenditures of smokers andnonsmokers for all articles was 0.95. Removing an article in which nonsmokers included former smokers20 and
one in which smokers did not include former smokers,26
as well as an article including females,26 those excluding
medical expenditures of inpatients,23, 28 and one excluding dental expenditures29 showed no notable effects.
Table 2 indicates weighted geometric mean of ratios
between age-adjusted mean medical expenditures ofsmokers and nonsmokers according to insurance group.
When medical insurance beneficiaries as study subjects
were divided by type of insurance (a) National Health
Insurance (NHI) and Government-Managed Health In-

surance (GMHI) and (b) Society-Managed Health Insurance (SMHI), the geometric mean ratio of group (a) was
somewhat greater than 1.0 (Table 2-A) and that of group(b) was considerably less than 1.0 with statistical significance (Table 2-B). A similar division into (c) NHI and(d) GMHI and SMHI gave similar results (Table 2-CD).
Pearson’s chi-square tests for 2x2 contingency tablesof (i) study subjects {group (a) or (b)} and mean age(-49 or 50+ years old) and (ii) study subjects {group (a)or (b)} and the medical expenditure ratio (<1.0 or 1.0≦)
were statistically significant (both p<0.01, Yates’ correction: p<0.05). This means that (a) NHI and GMHI beneficiaries are older than (b) SMHI beneficiaries and thatthe ratio of group (a) is greater than that of group (b).
The two 2x2 contingency tables with statistical tests areshown in Table 3.
In the above, the standard population for age-adjustment was the total population of smokers and nonsmokers by age group in each article. The calculation was
also conducted using the male census population in Japan in 1995 as the standard population for age-adjustment, and the results were nearly equal to those using the
population by age group in the articles cited in the present study. The mean calendar year of submission ofhealth insurance claims in the 11 studies selected in thepresent study was 1995.
The results of analysis including duration of submission of health insurance claims were almost same as
those not including the duration.
In the above, current and former smokers were treatedas smokers. Ratios of values between current smokers

Shimada N, et al: Medical expenditure of smokers

56

Table 2 Geometric Mean of Ratios of Mean Medical Expenditures between
Smokers and Nonsmokers
Articles for meta-analysis

Reference number

Geometric mean Ratio

A) NHI and GMHI
B) SMHIC) NHI
D) GMHI and SMHI

19, 21, 23, 26-28
20, 22, 24-25, 29
19, 21, 23, 26-27
20, 22, 24-25, 28-29

1.06
0.90
1.03
0.92

Abbreviations: GMHI: Government-Managed Health Insurance,
NHI: National Health Insurance,
SMHI: Society-Managed Health Insurance

and nonsmokers were also calculated. The difference inthe geometric mean ratios between (i) current smokers
versus nonsmokers and (ii) current and former smokers
versus nonsmokers of NHI and GMHI group was not notable.
Discussion
Increases in the incidence and mortality rates of many
diseases due to smoking have been reported in numerous
epidemiologic studies and described in many textbooks.
There are many studies using the indirect method1-15 indicating marginal increases in medical expenditures ofsmokers calculated indirectly from odds or hazard ratios
between smoking and incidence and/or mortality rates
cited from these epidemiologic studies. The odds or hazard ratios are much greater than 1.0. On the other hand,
medical expenditures of smokers and nonsmokers weredirectly observed and the excessive medical costs bysmoking were calculated in a number of studies using
the direct method.1 6-2 9 Some studies using the direct
method reported that medical expenditures of smokers
were less than those of nonsmokers while other studies
using the direct method reported greater expenditures.
In the present study, we compared age-adjusted medical expenditures between smokers and nonsmokers instudies using the direct method conducted in Japan. The
age-adjusted geometric mean ratio of Society-Managed
Health Insurance (SMHI) with small numbers of elderly
persons was less than 1.0 (Table 2-B) and the value of
National Health Insurance (NHI) and Government-Managed Health Insurance (GMHI) with many elderly persons was greater than 1.0 (Table 2-A). Table 3 showsthat most ratios of medical expenditures between smokers and nonsmokers for insurance groups with many elderly individuals were greater than 1.0, while all ratios
for insurance groups with small numbers of elderly individuals were less than 1.0. This does not indicate thatthe mean medical expenditure of smokers is actually
greater than that of nonsmokers.
The ratio of mean medical expenditures between smok-

ers and nonsmokers is divided into elements due tosmoking and elements other than smoking. Poor healthdue to smoking is apt to appear many years after the startof habitual smoking, i.e., the influence of smoking on
the ratio of younger persons is very small and aging increases the ratio. Many younger smokers are not yet inbad health, while many elderly smokers are in worse
health than elderly nonsmokers. The elements due tofactors other than smoking coincide with selection bias
from the viewpoint of investigating the influence ofsmoking on the ratio. These elements can be divided
into two parts, one which increases by age and the otherwhich remains constant. The latter corresponds to an intercept of regression and the former corresponds to aslope of regression. The slope means that the ratio ofyounger persons is less than 1.0 and the ratio of elder
persons is greater than 1.0. Generally the ratios of medical expenditure between smokers and nonsmokers for

Table 3 Two 2x2 Contingency Tables for (i) Insurance Group andMean Age and (ii) Insurance Group and the Mean Medical Expenditure
Ratio between Smokers and Nonsmokers
Table for the Insurance Group and Mean Age (i)Insurance group
NHI and GMHI
SMHI

Mean age (years)
50+
-49
0
6
4
1

Pearson: p<0.01, Yates: p<0.05
Abbreviations: GMHI: Government-Managed Health Insurance,
NHI: National Health Insurance,
SMHI: Society-Managed Health Insurance
Table for the Insurance Group and the Ratio (ii)
Insurance group
NHI and GMHI
SMHI

Medical expenditure ratio
<1.0
1.0≦
1
5
5
0

Pearson: p<0.01, Yates: p<0.05Keio J Med 2007; 56 (2): 53－ 60

57

Fig. 1 Scheme of the ratio of mean medical expenditure between smokers and nonsmokers by age with factors which influence theratio.

groups including many elderly individuals are greaterthan 1.0, while the ratios for groups with small numbersof elderly individuals are less than 1.0 (Tables 2-3). Thisshows the presence of “smokers’ indifference to health,”
meaning that smokers seldom receive medical care even
if they recognize morbidness and reluctantly receive careafter they recognize severe symptoms and/or signs.
Smoking was detected as a risk factor in diabetes mellitus in some epidemiologic studies.3 4, 3 5 It is noted thatthe personality of diabetes patients is often carefree.36, 37
Smokers’ indifference to health must decrease medical
expenditure of younger smokers and increase that of elder smokers. The intercept means that the ratio is not
greater than 1.0 in the present study, having no relation
to age. It is not determined that mean medical expenditure of smokers is greater than that of nonsmokers, inspite of poor health due to smoking. This shows a“healthy smoker effect,” meaning that healthy persons
who are not in poor health due to smoking can start andcontinue to smoke habitually, analogous to the “healthy
worker effect” in the occupational health field. Factors
which influence the medical expenditure ratio are (i)smoking, (ii) smokers’ indifference to health, and (iii)
healthy smoker effect.
A scheme in which these findings are expressed isshown in Fig. 1. In Fig. 1, the transverse which intersects at 1.0 of the ordinate is the level of nonsmokers.
The figure shows the actual medical expenditure ratio by
age with three factors which influence the ratio. The
three factors are (i) smoking, (ii) smokers’ indifference

to health, and (iii) healthy smoker effect. The sum of thethree factors is equal to the actual ratio. The dotted line
in Fig. 1 shows a hypothetic ratio if smokers did notsmoke. The scaling of the ordinate is not known, so thelinearity or curvature of the lines or curves is not known.
In the present study, the three factors have not been verified. Therefore, the presence of the three factors should
be strictly verified and their magnitude estimated in the
future. Excessive medical expenditures of smokers inthe studies using the indirect method must be derived
from smoking and smokers’ indifference to health.
The difference in the age-adjusted geometric mean ratios between (a) the NHI and GMHI group (Table 2-A)and (b) the SMHI group (Table 2-B) was notable because of age difference. In the present study, the main
effect is smoking status, i.e., smokers or nonsmokers,
and age is a significant interaction. It should be notedthat when interaction is significant the main effect is often meaningless.
In the present study, the age-adjusted medical expenditure ratios between smokers and nonsmokers were investigated from studies using the direct method conductedin Japan. Studies using direct estimation16-18 conductedin countries other than Japan were not used. The definitions of medical expenditures, medical service systems
including medical security systems, socioeconomic status, and cultural background in the articles were notably
different from those of the present study. Differencesamong medical expenditures under different conditions
are not meaningful. Therefore, comparing medical ex-

58

penditure ratios between smokers and nonsmokers ofmany countries is not appropriate.
The proportions of medical expenditures for inpatients
per total medical expenditure in 1985 and 1995 were
44.2% and 36.8%, respectively. 3 8 These values are
great, while the number of inpatients is somewhat lessthan that of outpatients. The medical expenditures for
inpatients were not included in two studies23, 28 in which
the subjects were NHI and GMHI beneficiaries. In particular, the annual per capita medical expenditure of Nakagaki’s article28 excluding inpatients was very low (Table 1). The variations of the ratios must be enlarged
when the medical expenditures for inpatients are included.
In the present study, we treated current smokers andformer smokers as smokers in principle. The reasons are
as follows. Current smoking affects lifestyle-related diseases after many years. It cannot be denied that one of
the causes of diseases for former smokers is their pastsmoking when they are taken ill. Therefore, we investigated differences in medical expenditures of persons
with and without smoking experience in the present
study. Many studies using this comparison have been
published.
A lot of studies reported that the medical expendituresof former smokers were larger than those of current
smokers. In Kondou’s study,2 0 nonsmokers included
former smokers. This shows that the ratio of the article20
may be somewhat less than that of current and former
smokers versus nonsmokers. In Fujimoto’s study, 2 6
however, the medical expenditure of former smokers
was less than that of current smokers. Therefore, themedical expenditure ratio including current and former
smokers is less than the value in the article2 6 excluding
former smokers.
It was revealed that the dental expenditures of smokers
were larger than those of nonsmokers.20 Dental expenditure was removed in Urano’s article,29 indicating that the
medical expenditure ratio in the article2 9 may be lessthan the value including dental expenditures. The proportion of dental expenditures per total medical expenditures was small, 8.8% in 1995.38
In Table 1, the ratios are distributed widely; in particular the ratio of one article21 for NHI is less than those of
the other articles for the same type of insurance. The
reasons for the variation in medical expenditure ratio are
as follows. (i) Many articles included medical expenditures of inpatients or dental expenditures while a few23, 29
did not. (ii) Former smokers were treated as smokers inmany articles, while former smokers were treated asnonsmokers in one article2 0 and excluded in another.2 6(iii) The durations of submission of health insurance
claims differed notably and the range of submission year
were distributed widely. (iv) When high cost medical
expenditures were defrayed for a few patients, the mean

Shimada N, et al: Medical expenditure of smokers

medical expenditure of the group including such patients
increased dramatically. The most important element of
the variation in the medical expenditure ratio is the increase in medical expenditure due to a few high cost patients. The variation in medical expenditure was indicated to be very large in one figure.19 In Table 1, the annual per capita medical expenditure of Nakagaki’s article28
excluding inpatients shows an especially low value,
while very expensive values are shown in some articles
including inpatients. In this study area, the medical expenditure ratio excluding high cost patients may be stable, but the significance of the ratio must be poor fromthe viewpoint of medical economics. In order to obtaina stable medical expenditure ratio, too many study subjects are necessary. In this study area, dramatically elevated medical expenditure due to a few high cost patients
is a very troublesome problem for obtaining stable values.
A very heavy right tail was indicated as a characteristicof medical expenditure distribution.1 9 The most important element of the large variation in the medical expenditure is the increase in medical expenditure due to a few
high cost patients. The mean medical expenditures ofnonsmokers were distributed widely in Table 1. Especially, the annual per capita medical expenditure of Nakagaki’s article2 8 excluding inpatients was very low (Table 1). In order to compare the mean medical expenditure of smokers with that of nonsmokers, a difference
between the two values is inappropriate, but a ratio is appropriate. Therefore, in the present study, the ratios between the mean medical expenditures of smokers andnonsmokers were calculated.
Differences in the ratios and the mean ages between(a) the NHI and GMHI group and (b) the SMHI groupwere statistically significant (Table 3), meaning that (a)and (b) groups were different from each other qualitatively. Therefore, calculating geometric mean ratio using the ratios including all studies is not appropriate.
However, the geometric mean ratio for all studies is significant only in sensitivity analysis, e.g. confirming
slight influence of treatment of former smokers, including female subjects, and excluding inpatients and dental
expenditures. This does not mean, however, that obtaining geometric mean ratio from the ratios of (a) the NHI
and GMHI group or (b) the SMHI group separately is inappropriate, because each (a) or (b) group is not heterogeneous from the viewpoint of social backgrounds andages of the insurance beneficiaries.
The purpose of the present study is to investigate theratios between mean medical expenditures of smokers
and nonsmokers from studies conducted observing medical expenditure directly in Japan as cross-sectional studies. It was reported3 9, 4 0 that innovations in medical
technologies and improvement of life-style e.g. smoking
cessation would lead to decrease the medical expendi-

Keio J Med 2007; 56 (2): 53－ 60tures in the short term, but to increase the cumulative
medical expenditures in the long term in other developed
countries than Japan. Studies on the life-time medical
expenditures according to smoking experience should be
conducted in Japan, making it possible to compare themedical expenditures of smokers and nonsmokers inshort term and life-time.
In the present study, the influence of smoking on medical expenditures was investigated using published articles of studies conducted directly observing medical expenditures of smokers and nonsmokers in Japan. Mortality, incidence, and prevalence rates of lifestyle-relateddiseases and population medical expenditures are fast increasing30, 31 due to the rapid aging of society in Japan.32
The national and local governments in Japan are in financial difficulties. Smoking-related diseases are typicalamong lifestyle-related diseases. Therefore, the present
study is significant in light of this recent socioeconomic
condition in Japan from the viewpoint of public health.
The present study does not indicate that medical expenditure of smokers is actually greater than that of nonsmokers. This does not mean that lower quality of life
(QoL) and premature death of smokers can be neglected.
Acknowledgment
This is a modified version of papers presented at the
15th Meeting of the Japan Epidemiological Association,
2005, Otsu, Japan. This research was supported in partby a grant from the Smoking Research Foundation in theyear 2005. We express deep appreciation to Prof. Tadao
Miyakawa at the International School of Economics, Reitaku University for his support.
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