Ecological Studies Susan R' Tortolero, Ph'D'

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Ecological StudiesSusan R. Tortolero, Ph.D.
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Ecological Studies

• Looks for an association (correlation) between
  exposure rates and disease rates among groups or
  populations
• Disease data may include incidence rates,
  prevalence, or mortality for multiple or
  different defined populations
• Data on exposure need to be available for the
  same population and can include measures of
  economic development, environmental measures,
  measures of lifestyle
• The unit of observation is the population or
  community

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Ecological Studies

• Purposes include
• Generating hypotheses for further study
• Testing a hypothesis for further study (rarely
  done)

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Geographical comparisons

• One approach is to examine geographical
  correlations between disease incidence or
  mortality and the prevalence of risk factors.
• For example, mortality from coronary heart
  disease in local authority areas of England and
  Wales has been correlated with neonatal mortality
  in the same places 70 and more years earlier.
  This observation generated the hypothesis that
  coronary heart disease may result from the
  impaired development of blood vessels and other
  tissues in fetal life and infancy.
• Although useful observations have been found from
  geographical analyses, there is a need to be
  careful about the interpretation. Confounding by
  age and sex-- may need to need to standardize.
• Biases can occur if ascertainment of disease or
  exposure, or both, differs from one place to
  another.  

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Time trends

• Many diseases show remarkable fluctuations in
  incidence over time.
• If time or secular trends in disease incidence
  correlate with changes in a community's
  environment or way of life then the trends may
  provide important clues to etiology.
• For example the increasing incidence of melanoma
  has been linked with greater exposure to sunlight
  
• Successive rises and falls in mortality from
  cervical cancer have been related to varying
  levels of sexual promiscuity, as evidenced by
  notification rates for STDs.
• May be biased by differences in the ascertainment
  of disease. (e.g., as health services have
  improved, diagnostic criteria and techniques have
  changed).  

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BMJ 19983161047-1051 ( 4 April ) Papers Ecolog
ical study of reasons for sharp decline in
mortality from ischaemic heart disease in Poland
since 1991 Witold A Zatonski, professor, a
Anthony J McMichael, professor, b John W Powles,
lecturer. c Objective To investigate the
reasons for the decline in deaths attributed to
ischaemic heart disease in Poland since
1991 after two decades of rising rates. Design
Recent changes in mortality were measured as
percentage deviations in 1994 from rates
predicted by extrapolation of sex and age
specific death rates for 1980-91 for diseases of
the circulatory system and selected other
categories. Available data on national and
household food availability, alcohol consumption,
cigarette smoking, socioeconomic indices, and
medical services over time were reviewed. Main
outcome measures Age specific and age
standardised rates of death attributed to
ischaemic heart disease and related causes.
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Results The change in trend in mortality
attributed to diseases of the circulatory system
was similar in men and women and most marked
(gt20) in early middle age. For ages 45 to 64 the
decrease was greatest for deaths attributed to
ischaemic heart disease and atherosclerosis
(around 25) and less for stroke (lt10). For most
of the potentially explanatory variables
considered, there were no corresponding changes
in trend. However, between 1986-90 and 1994 there
was a marked switch from animal fats (estimated
availability down 23) to vegetable fats (up 48)
and increased imports of fruit. Conclusion
Reporting biases are unlikely to have exaggerated
the true fall in ischaemic heart disease neither
is it likely to be mainly due to changes in
smoking, drinking, stress, or medical care.
Changes in type of dietary fat and increased
supplies of fresh fruit and vegetables seem to be
the best candidates.
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Migrant Studies

• Offers a way of discriminating genetic from
  environmental causes of geographical variation in
  disease
• May also indicate the age at which an
  environmental cause exerts its effect.
• For example, 2nd generation Japanese migrants to
  the USA have substantially lower rates of stomach
  cancer than Japanese people in Japan, indicating
  that the high incidence of the disease in Japan
  is environmental in origin.
• If first generation migrants rates are
  intermediate, it may suggest that the adverse
  environmental influences act, at least in part,
  early in life.
• In interpreting migrant studies it is important
  to bear in mind the possibility that the migrants
  may be unrepresentative of the population that
  they leave, and that their health may have been
  affected directly by the process of migration.

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Migrant Studies (Continued)

• Norwegian immigrants into the US have been found
  to have a higher incidence of psychosis than
  people in Norway. Although this may indicate
  environmental influences in the USA that led to
  psychotic illness, it may also have resulted from
  selective immigration from Norway of people more
  susceptible to mental illness, or from the
  unusual stresses imposed on immigrants during
  their adjustment to a foreign culture.

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Occupation and social class

• The other populations for whom statistics on
  disease incidence and mortality are readily
  available are occupational and socioeconomic
  groups.
• For example,
• mortality from pneumonia is high in welders,
• The steep social class gradient in mortality from
  chronic obstructive lung disease is evidence that
  correlates of poverty, perhaps bad housing, have
  an important influence on the disease.

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BMJ 19963121004-1007 (20 April) Papers
Income distribution and mortality cross
sectional ecological study of the Robin Hood
index in the United States Objective To
determine the effect of income inequality as
measured by the Robin Hood index and the Gini
coefficient on all cause and cause specific
mortality in the United States. Design Cross
sectional ecological study. Setting Households
in the United States. Main outcome measures
Disease specific mortality, income, household
size, poverty, and smoking rates for each state.

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Results The Robin Hood index was positively
correlated with total mortality adjusted for age
(r0.54 Plt0.05). This association remained after
adjustment for poverty (Plt0.007), where each
percentage increase in the index was associated
with an increase in the total mortality of 21.68
deaths per 100000. Effects of the index were also
found for infant mortality (P0.013) coronary
heart disease (P0.004) malignant neoplasms
(P0.023) and homicide (Plt0.001). Strong
associations were also found between the index
and causes of death amenable to medical
intervention. The Gini coefficient showed very
little correlation with any of the causes of
death. Conclusion Variations between states in
the inequality of income were associated with
increased mortality from several causes. The size
of the gap between the wealthy and less well
off--as distinct from the absolute standard of
living enjoyed by the poor--seems to matter in
its own right. The findings suggest that policies
that deal with the growing inequities in income
distribution may have an important impact on the
health of the population.
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BMJ 1998316741-745 ( 7 March )Use of calcium
channel blockers and risk of suicide ecological
findings confirmed in population based cohort
study Gunnar Lindberg, clinical
epidemiologist, a Kerstin Bingefors, senior
lecturer, b Jonas Ranstam, biostatistician, a
Lennart Råstam, professor, c Arne Melander,
professor. a a Swedish Network for Pharmaco-
epidemiology, Foundation, Malmö University
Hospital, SE-205 02 Malmö, Sweden, b Department
of Pharmaceutical Services Research, Uppsala
University, Box 586, SE-751 23 Uppsala, Sweden,
c Department of Community Medicine, Lund
University, Malmö University Hospital, SE-205
02 Malmö Objective To investigate possible
associations between use of cardiovascular drugs
and suicide. Design Cross sectional ecological
study based on rates of use of eight
cardiovascular drug groups by outpatients. A
population based cohort study including users of
drugs to control hypertension. Subjects The
ecological study included 152 of Sweden's
284 municipalities. The cohort study included all
inhabitants of one Swedish municipality who
during 1988 or 1989 had purchased cardiovascular
agents from pharmacies within the municipality.
Six hundred and seventeen subjects (18.2) were
classified as users of calcium channel blockers
and 2780 (81.8) as non-users. Main outcome
measures Partial correlations (least squares
method) between rates of use of cardiovascular
drugs and age standardised mortality from suicide
in Swedish municipalities. Hazard ratios for risk
of suicide with adjustments for difference in age
and sex in users of calcium channel blockers
compared with users of other hypertensive drugs
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. Results Among the Swedish municipalities the
use of each cardiovascular drug group except
angiotensin converting enzyme inhibitors
correlated significantly and positively with
suicide rates. After adjustment for the use of
other cardiovascular drug groups, as a substitute
for the prevalence of cardiovascular morbidity,
only the correlation with calcium channel
blockers remained significant (r0.29, Plt0.001).
In the cohort study, five users and four
non-users of calcium channel blockers committed
suicide during the follow up until the end of
1994. The absolute risk associated with use of
calcium channel blockers was 1.1 suicides per
1000 person years. The relative risk, adjusted
for differences in age and sex, among users
versus non-users was 5.4 (95 confidence interval
1.4 to 20.5). Conclusions Use of calcium
channel blockers may increase the risk of suicide.
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BMJ 1995311226-230 (22 July) Papers
Relation between parasuicide, suicide,
psychiatric admissions, and socioeconomic
deprivation David J Gunnell, lecturer in public
health medicine and epidemiology,a Tim J Peters,
senior lecturer in medical statistics,a Robert M
Kammerling, consultant in public health
medicine,b Jane Brooks, NHS data analyst a
Objective To examine the relations between
parasuicide, suicide, psychiatric inpatient
admissions, and socioeconomic deprivation.
Design Ecological analysis with data from
routine information systems and the 1991 census.
Setting 24 localities in the area covered by
the Bristol and District Health Authority
(population 817000), consisting of aggregations
of neighbouring wards, with an average population
of 34000. Subjects 6089 subjects aged over 10
years admitted to hospital after parasuicide
between April 1990 and March 1994 997 suicides
occurring 1982-91 4763 subjects aged 10-64 years
admitted with acute psychiatric illness between
April 1990 and March 1994.
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Results Localities varied significantly in
standardised admission ratios for parasuicide and
standardised mortality ratios for suicide
(Plt0.001). Spearman's rank correlation
coefficient between the standardised mortality
ratio for suicide and standardised admission
ratio for parasuicide was 0.73 (95 confidence
interval 0.46 to 0.88). Correlation between
parasuicide and Townsend score was 0.86 (0.70 to
0.94) and between suicide and Townsend score 0.73
(0.46 to 0.88). The partial correlation
coefficient between suicide and parasuicide after
the Townsend score was adjusted for was 0.29
(-0.13 to 0.62). The correlation between
standardised admission ratio for parasuicide and
standardised admission ratio for psychiatric
illness was 0.76 (0.51 to 0.89) and between
standardised mortality ratio for suicide and
standardised admission ratio for psychiatric
illness was 0.72 (0.45 to 0.87). Conclusion A
strong ecological association exists between
suicide and parasuicide, with socioeconomic
deprivation accounting for much of this relation.
This strong association provides supporting
evidence for the importance of social policy
measures in attaining Health of the Nation
targets on mental health.