Health Studies

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Health Studies

• York Region Health Services Department
• Health Protection Division
• June 14, 2007

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The Role of Health Services

• To promote and protect the health of the
  population
• Under the HPPA, when a complaint is made that an
  occupational or environmental health hazard
  exists, the health department shall.investigate
  the complaint to determine whether the health
  hazard exists or does not exist
• Use evidence-based research to support public
  health activities

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Evidence-Based Public Health

• What is evidence-based public health?
• The use of evidence that has been derived from a
  variety of health and social science methods
  including population health assessment,
  surveillance, research and evaluation methods -
  to arrive at judicious decisions on public health
  policies and best practices

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Sources of Evidence

• Epidemiological (Health) studies
• Descriptive review of routinely collected data
• Analytical
• Environmental monitoring
• Ministry of Environment does testing and
  determines if standards are being met

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What is a Health Study?

• No official definition
• In the context of epidemiology, a study refers
  to
• The use of tested and validated methods of
  scientific inquiry, including surveillance,
  observation, hypothesis testing, analytic
  research and experiments

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Epidemiological (Health) Study

• There are two categories of epidemiologic studies
• Descriptive studies describe distributions of
  disease, injury or health in a population
• Analytic studies test hypotheses about causes of
  disease, injury or health or the effectiveness of
  interventions

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Study Designs

• Descriptive
• Case reports or case series
• Cross-sectional or prevalence surveys
• Correlational or ecologic studies

• Analytic
• Case-control
• Cohort
• Trials (involve interventions)
• Clinical
• Preventive
• Community intervention

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Cross-Sectional/Prevalence

• Advantages
• Compare regions and trends over time (if
  repeated)
• Data is readily available (although not always
  current)
• Limitations
• More likely to detect cases of long duration as
  opposed to short duration
• Care must be taken in generalizing the results to
  ensure that the general population is similar to
  the study population
• It is not possible to tell whether the outcome
  preceded the exposure

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Case-Control Studies

• Case-control studies are used in determining the
  causes of diseases, injuries and illness. 
• They are particularly valuable for
• Studying rare conditions
• Testing hypotheses quickly and relatively cheaply
  
• Determining whether one outcome is related to
  multiple exposures
• There are, however, potential problems to
  consider
• Ability of subjects to remember past exposure
  information
• Identifying an appropriate control group
• Controlling for the influence of confounding
  variables

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Cohort Studies

• Cohort studies are valuable for the following
• Exposure variables are documented to precede
  outcomes
• One exposure can be related to multiple outcomes
• Actual incidence rates of outcomes can be
  determined
• An efficient way to study rare exposures
• The difficulties with cohort studies
• Extensive resources are needed (both money and
  personnel)
• Large numbers of subjects are required
• Long follow-up periods are needed
• Potential for subjects to leave or drop out of
  the study

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Other Sources of Evidence

• Population Health Assessments
• Health Surveys
• Cluster Investigations

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Population Health Assessments

• Includes measuring, monitoring and reporting on
  the
• status of a populations health
• Generally, a report based on cross-sectional or
• prevalence data
• Use of rates (number of events in a population)
  to
• compare populations

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Health Surveys

• Public health surveillance is the ongoing,
  systematic collection, analysis and
  interpretation of health and behavioural data and
  the timely dissemination of these data to those
  who need to know
• Example Rapid Risk Factor Surveillance System
  collects local data on behavioural risk factors
  (e.g. pesticide use, food consumption)

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Cluster Investigations

• Can include cancer, birth defects, other
  non-infectious diseases/conditions
• Actual clusters are rare
• Many issues in conducting these investigations
• Small sample size
• Hard to determine statistical significance
• Lack of recent, available data

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Criteria to Conduct a Study

• Is there evidence that a problem exists?
• This is established by assessing the distribution
  of health determinants, health status and disease
  incidence, which are derived from provincial and
  local data sets
• These analyses use specific information on
• Demographics
• Burden of illness, including mortality and
  morbidity rates
• Reproductive outcomes
• Risk factor prevalence
• Health conditions (including injury and substance
  misuse)
• Environmental conditions and hazards
• Other health determinants

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Data Sources

• Registries (e.g. Ontario Cancer Registry)
• Ministry of Health Long-Term Care databases
  (OHIP records, hospitalizations (in-patient,
  emergency visits, day procedures), vital
  statistics, birth defects, etc.)
• Health Surveys (e.g. Rapid Risk Factor
  Surveillance System, Canadian Community Health
  Survey)

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In Summary

• The need for public health action must be
  supported by describing the magnitude, severity
  and preventability of public health issues
• The public health actions that are taken should
  be determined by identifying options for action
  and the relative effectiveness of specific
  interventions

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Questions?