Body Mass Index and Health Service Utilization, Reidpath et al.
(n ϭ 194), for instance, observed higher healthcare use with
increasing BMI (15). This relationship was also observed in
a much larger study (n ϭ 17,118) based on a survey of
members of a health-service organization (16). It is note-
worthy that there are few large survey studies using repre-
sentative samples (17–19). Where the studies do exist, they
are limited geographically and often, though not exclu-
sively, limited to a subpopulation. Fontaine et al. (19), for
example, studied only women, and Brown et al. (17) limited
their study to women 45 to 49 years of age. The study by
Trakas et al. (18) is the only existent study of health-service
use based on a nationally representative sample, and this
study did not include the use of preventive health services.
Improved knowledge about the impact of obesity on
health services requires more research based on nationally
representative samples that specifically examine health-ser-
vice use. This would supplement and enhance the economic
analyses that already exist. The aim of the present study is
to examine the relationship between BMI and the use of
medical and preventive health services based on data from
the 1995 Australian National Health Survey (20).
To understand the context of the present study, one
needs to understand that Australia uses a primary-health-
care model. Visits to specialists occur generally with only
a referral from general (medical) practitioners; costs are
subsidized (sometimes up to 100%) through a universal
healthcare system (“Medicare”) that covers all citizens,
permanent residents, and some temporary residents. The
healthcare is partially funded through a national levy on
income and covers such things as essential drugs, non-
elective medical procedures in public hospitals, and visits
to medical practitioners.
grams) by the square of their self-reported height
(meters). A categorical measure of BMI was also derived
according to specifications defined by the Australian
National Health and Medical Research Council (21). The
four BMI categories were: underweight (Ͻ20 kg/m2);
normal weight (20 to 25 kg/m2); overweight (Ͼ25 to 30
kg/m2); and obese (Ͼ30 kg/m2).
Participants in the National Health Survey were asked
about their use of a range of health services in the 2 weeks
before the interview, including hospitalization, admission to
a hospital accident and emergency department, visits to
outpatient clinics (i.e., a visit to a hospital clinic that does
not involve admission, such as attendance at a pain man-
agement clinic, or attendance at a hospital clinic to receive
physical therapy), visits to doctors, and visits to other health
professionals. Participants also reported whether they had
used any medications in the last 2 weeks. Women were
additionally asked about their use of preventive health ser-
vices including mammography, manual breast examination,
and Papanicolaou (pap) smears. Responses to these latter
questions were reduced to binary outcomes according to
whether a woman had a pap smear or a breast examination
in the last 2 years. Mammography outcomes were similarly
classified, but only for women Ն50 years of age.
Age was recorded by the Australian Bureau of Statistics
categorically in 5-year blocks. Estimated continuous age
was calculated by adjusting each participant’s age to the
midpoint of his or her age block.
A measure of income was calculated, which estimated the
income of the highest-earning individual in each partici-
pant’s family. Because income figures were recorded cate-
gorically in $5000 blocks in the survey, it was necessary to
adjust income to the midpoint of the income block.
Statistical Analysis
Research Methods and Procedures
The relationship between measures of health-service use
and BMI was tested using logistic regression models. Sep-
arate models were developed using the continuous or the
categorical measure of BMI as the predictor variables. Age
and estimated income were included in all models as control
variables. We developed separate models using continuous
and categorical BMI because of some evidence suggesting
that analyses using categorical BMI (unlike continuous
BMI), based on self-reported height and weight, may have
unreasonably high levels of systematic error (22–25).
In the regression models using categorical BMI, the
normal-weight group (BMI, 20 to 25 kg/m2) was used as
the reference category. In the regression models using
continuous BMI, participants with a BMI of Ͻ20 kg/m2
were excluded, because of the anticipated nonlinear
relationship (17).
Data
This study involved a secondary analysis of data from the
1995 Australian National Health Survey (20). The survey
was the most recent in a series of health surveys conducted
by the Australian Bureau of Statistics. It utilized a multi-
stage cluster sample of households in all six Australian
states and two territories. Information was obtained by
personal interviews. The total survey sample was 53,790
individuals (26,434 men and 27,356 women) representing a
response rate of ϳ97%. The present study was limited,
however, to adults Ն20 years of age (n ϭ 37,616). With the
exclusion of the 6.4% of cases with missing information
regarding height, weight, and/or income data, the working
sample was 35,207 (17,033 men and 17, 174 women).
Measures
National Health Survey participants were asked for
their height and weight. Continuous BMI was calculated
by dividing a participant’s self reported weight (kilo-
Results
The percentage of men and women in this Australian
study that reported using the medical or preventive health
OBESITY RESEARCH Vol. 10 No. 6 June 2002 527