HOW TO TEACH BASICS
IN
OCCUPATIONAL EPIDEMIOLOGY
Guido F. MOENS
•Dept. Occupational & Environm. Medicine, Catholic University of Leuven,
Leuven (Belgium)
•Dept. Research & Development, Occupational Health Services IDEWE,
Leuven (Belgium)
EASOM Summerschool, Bari (IT), 1-9-2006
Overview
1.
2.
3.
4.
5.
Teaching framework
Teaching objectives
Teaching method & format
Teaching content
Specific content issues
•
•
Political & ethical issues
Major methodological issues
6. Evaluation / timetable
7. Limitations
EASOM Summerschool, Bari (IT), 1-9-2006
1. TEACHING FRAMEWORK
1.1. Trainees/students:
• Post-academic level students :
during the 2-year theoretical training in OM
for MaMed graduates (former MD)
• Other groups :
during the training for agreed O. Hygienists
• Previous knowledge of epidemiology :
= poor or none
= BASICS
EASOM Summerschool, Bari (IT), 1-9-2006
1. TEACHING FRAMEWORK
1.2. Teacher:
Professional situation / expertise :
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•
•
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Epidemiologic researcher since 30 years
University teacher in OE since 15 years
Epidemiologist in OHS since 18 years
Director R&D in OHS since 6 years
Experience with / access to
practice-linked studies/data e.g.:
• Standard registration data
•
(collected during the periodical medical examinations)
Surveys by OPh
e.g. stress at work, MSD, …
EASOM Summerschool, Bari (IT), 1-9-2006
Overview
1.
2.
3.
4.
5.
Teaching framework
Teaching objectives
Teaching method & format
Teaching content
Specific content issues
•
•
Political & ethical issues
Major methodological issues
6. Evaluation / timetable
7. Limitations
EASOM Summerschool, Bari (IT), 1-9-2006
2. TEACHING OBJECTIVES
Trainees should be able to :
1. Assess the role of E. for OM and for OM-practice:
Know the
= Objectives of OE
= Strengths and limitations in solving workplace
health problems
= Key features of OE, distinguishing it from other
fields of E.
EASOM Summerschool, Bari (IT), 1-9-2006
2. TEACHING OBJECTIVES
Objectives of OE:
1. Describe the occurrence & characteristics of
2.
3.
(work-related) health problems among workers
Identify hazardous workplace exposures to prevent
O. disease (examples of successful prevention)
Provide information for
•
•
Risk assessment
Prevention in the general population
e.g. health effect of low exp. levels of pesticides
--> estimation from exposed workers
4. Assess the effect of workplace interventions
e.g. replacement of asbestos by MMF
EASOM Summerschool, Bari (IT), 1-9-2006
2. TEACHING OBJECTIVES
Trainees should be able to :
2. Design and perform small OE-study
•
•
•
•
•
•
Write a study protocol (draft)
Discuss E. research questions with professionals and
lay people from OH-practice
Collect and analyse data properly
Report OE-findings (communication)
Interpret and communicate findings from OE-literature
Cooperate with research centre in larger OE-study
EASOM Summerschool, Bari (IT), 1-9-2006
Overview
1.
2.
3.
4.
5.
Teaching framework
Teaching objectives
Teaching method & format
Teaching content
Specific content issues
•
•
Political & ethical issues
Major methodological issues
6. Evaluation / timetable
7. Limitations
EASOM Summerschool, Bari (IT), 1-9-2006
3. TEACHING METHOD & FORMAT
3.1. METHOD
• Practice-oriented / problem-based
approach
= application of E. methods in a real setting
= practical problems encountered in setting
up and performing an E. study
= interactive teaching
EASOM Summerschool, Bari (IT), 1-9-2006
3. TEACHING METHOD & FORMAT
3.1. METHOD
• Individual activity of students + group activity
e.g. drafting a study protocol
(about problem from one’s own practice)
= preparation of Master-dissertation
e.g. critical reading of E-papers
•
But, no time left for presentation/ discussion
of protocols
e.g with course coordinator
with other participants
with users (company, union)
EASOM Summerschool, Bari (IT), 1-9-2006
3. TEACHING METHOD & FORMAT
3.2. FORMAT
•
Incorporated into one course with
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•
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Medical statistics
Medical data handling (informatics)
Theoretical lectures and practical exercises
(individual/group) spread over two years
(13 hours + 13 hours = 26 hours)
•
Course notes
(containing questions and answers)
EASOM Summerschool, Bari (IT), 1-9-2006
Overview
1.
2.
3.
4.
5.
Teaching framework
Teaching objectives
Teaching method & format
Teaching content
Specific content issues
•
•
Political & ethical issues
Major methodological issues
6. Evaluation / timetable
7. Limitations
EASOM Summerschool, Bari (IT), 1-9-2006
4. TEACHING CONTENT
4.1. General introduction to E. methodology
4.2. Setting up an E. study :
• Importance of the study protocol
• Design of a draft study protocol
using a practical example :
Prevalence study on low back pain among
hospital workers
EASOM Summerschool, Bari (IT), 1-9-2006
4. TEACHING CONTENT
4.3. Sources of error in E. studies
•
•
Random error
Bias
- Selection bias
- Confounding
- Observation bias
4.4. Characteristics and design of questionnaires
EASOM Summerschool, Bari (IT), 1-9-2006
4. TEACHING CONTENT
4.5. Examples of types of E. studies
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•
Short introduction of each study type
Real world example for each study type
using questions to be answered,
from setting up the study,
analyzing the data,
to the interpretation of the findings.
(partly based on the K.Steenland book :
Case studies in OE)
EASOM Summerschool, Bari (IT), 1-9-2006
4. TEACHING CONTENT
4.5. Types of E. studies :
1. Prevalence study
2. (Retrospective) cohort study
3. Case-control study
4. Disease clustering
EASOM Summerschool, Bari (IT), 1-9-2006
4. TEACHING CONTENT
4.5. Types of E. studies
1. Prevalence study :
“Low back pain among hospital workers”
(most common study type in OH practice)
2. (Retrospective) cohort study :
“Risk of spontaneous abortion among VDT-users”
3. Case-control study
“Occupational exposure and end stage renal
disease”
Calculation of association-, and impact-parameters,
sources of bias and error, and the control for these
are discussed and illustrated working through the
examples.
EASOM Summerschool, Bari (IT), 1-9-2006
4. TEACHING CONTENT
4.5. Types of E. studies
4. Disease clustering
• How to investigate a disease cluster using a stepwise
investigation method
A cluster is usually a trigger / motivation for a formal E.
study
To avoid expensive, large, unnecessary (and mostly
negative) E. studies
--> FIRST:
Cluster investigation through 3 steps / 3 questions on
Outcome / Association / Exposure
EASOM Summerschool, Bari (IT), 1-9-2006
4. TEACHING CONTENT
4.5. Types of E. studies
4. Disease clustering
Cluster investigation through 3 steps / questions on
Outcome / Association / Exposure
1. Orientation
2. Quantification
3. Quantitative analysis
(aggregated level + control group)
If positive :
Formal E. study design
EASOM Summerschool, Bari (IT), 1-9-2006
4. TEACHING CONTENT
4. Disease clustering
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How to communicate about risk
(notion of risk perception)
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Two examples :
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Cluster of cancer cases among young nurses in a
hospital ward
Cluster of urogenital disorders among production
workers exposed to chromium
4.6. Assessment of E. papers
Critical assessment of two or three papers from peer reviewed
journals (+ research report)
(to be prepared by students)
EASOM Summerschool, Bari (IT), 1-9-2006
Overview
1.
2.
3.
4.
5.
Teaching framework
Teaching objectives
Teaching method & format
Teaching content
Specific content issues
•
•
Political & ethical issues
Major methodological issues
6. Evaluation / timetable
7. Limitations
EASOM Summerschool, Bari (IT), 1-9-2006
5. SPECIFIC CONTENT ISSUES
5.1. Political and ethical issues
• Controversies :
- Strengths and weaknesses of E. methodology
- Role in causal/risk assessment
- Role of social, economic, political influences
(e.g. asbestos debate, EM-fields-debate)
•
Warning :
(Undue) emphasis on criticism of publications
--> desillusion on the value of OE
versus
practical problems in setting up a study
(writing of protocol)
EASOM Summerschool, Bari (IT), 1-9-2006
5. SPECIFIC CONTENT ISSUES
Practical problems in setting up a study
(writing of protocol)
• Practical compromises
• No study can be perfect / definitive
• Contribution to the pool of knowledge
BALANCE OF EVIDENCE
• Pressure from interested parties to
- set up a study quickly, or
- delay a study or action
e.g. “further studies needed” ≠
delay of prevention
• Disclosing conflict of interest / sources of funding
EASOM Summerschool, Bari (IT), 1-9-2006
5. SPECIFIC CONTENT ISSUES
5.2. Major methodological issues
1. Healthy Worker Effect (HWE):
How to handle?
2. Exposure data:
Problem of historical exposure
Markers of internal dose /biological effect
3. Confounding
4. Specific study designs (see Content)
5. Use of routine data
EASOM Summerschool, Bari (IT), 1-9-2006
Overview
1.
2.
3.
4.
5.
Teaching framework
Teaching objectives
Teaching method & format
Teaching content
Specific content issues
•
•
Political & ethical issues
Major methodological issues
6. Evaluation / timetable
7. Limitations
EASOM Summerschool, Bari (IT), 1-9-2006
6. ASSESSMENT /
EVALUATION / TIMETABLE
6.1. Assessment of the students
• Year 1 : Classical examination
(oral with written preparation)
• Year 2 : Discussion with course coordinator
on a draft of a study protocol
• From 2006-2007 on :
also self teaching exercises in year 2
EASOM Summerschool, Bari (IT), 1-9-2006
6. ASSESSMENT /
EVALUATION / TIMETABLE
6.2. Assessment of the course content / format
(quality assessment)
Each year:
anonymous questionnaire filled in by students
on
- content
- format
- course notes
EASOM Summerschool, Bari (IT), 1-9-2006
Overview
1.
2.
3.
4.
5.
Teaching framework
Teaching objectives
Teaching method & format
Teaching content
Specific content issues
•
•
Political & ethical issues
Major methodological issues
6. Evaluation / timetable
7. Limitations
EASOM Summerschool, Bari (IT), 1-9-2006
7. LIMITATIONS
• Very poor basic knowledge of E. or
statistics among starters (MaMed)
• More time needed : e.g.
•
•
Public presentations / discussions
e.g. of protocol
More exercises
EASOM Summerschool, Bari (IT), 1-9-2006
7. LIMITATIONS
• Co-ordination / timing with other
subcourses (statistics, informatics) is not
always easy in practice
e.g. the statistics course has to be finished before the
analysis aspects of E. studies
e.g. discussion about the content of medical informatics
subcourse
EASOM Summerschool, Bari (IT), 1-9-2006
REFERENCES
• Olsen J, Saracci R, Trichopoulos D.
Teaching epidemiology: Chpt 11.
IEA, New York : Oxford Univ. Press, 2000.
• Steenland K.
Case studies in occupational epidemiology.
New York : Oxford Univ. Press, 1993.
EASOM Summerschool, Bari (IT), 1-9-2006
THANK YOU FOR YOUR ATTENTION!
ANY QUESTIONS?
EASOM Summerschool, Bari (IT), 1-9-2006
EASOM Summerschool, Bari (IT), 1-9-2006
5. SPECIFIC CONTENT ISSUES
5.2. Major methodological issues
1. Healthy Worker Effect (HWE)
= type of selection bias in comparing workers
outcome with general population outcome
because:
• Workers are healthier at hiring
• Selection of unhealthy workers out of the workforce.
Mostly discussed in the context of cohort (follow-up)
studies, but also present in other types (e.g. prevalence
studies)
EASOM Summerschool, Bari (IT), 1-9-2006
5. SPECIFIC CONTENT ISSUES
5.2. Major methodological issues
How to handle the HWE?
•
Use of appropriate comparison groups
(within the cohort = internal comparison)
but does not affect those lost to the workforce.
•
Limitation of the extrapolation of the findings.
EASOM Summerschool, Bari (IT), 1-9-2006
5. SPECIFIC CONTENT ISSUES
5.2. Major methodological issues
2. Exposure data
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Estimation of historical exposure = difficult
Personal information/ interview/ records
on work history, causes:
- Recall bias
- Other forms of reporting bias
Job exposure matrices
(but also based on personal job information)
Real life examples to show the problems involved
EASOM Summerschool, Bari (IT), 1-9-2006
5. SPECIFIC CONTENT ISSUES
2. Exposure data
•
Molecular E. methods = markers of internal dose /
biological effect
but
major limitations for historical exposure
(only last weeks or months)
Choice of most appropriate method =
varies from study to study
EASOM Summerschool, Bari (IT), 1-9-2006
5. SPECIFIC CONTENT ISSUES
5.2. Major methodological issues
3. Confounding
•
Could be present in all E. studies but the
association with exposure and outcome must be
strong in OE
e.g. exposed (manual) workers usually will have
the same distribution of lifestyle factors (e.g.
smoking) as non-exposed (manual) workers
•
Complex mixtures (e.g. welding fumes)
--> identification problem
EASOM Summerschool, Bari (IT), 1-9-2006
5. SPECIFIC CONTENT ISSUES
5.2. Major methodological issues
4. Study designs :
Specific methodological issues and
characteristics
e.g. due to the OH-situation, cohort studies are more
common (most occupational exposures are rare in general
population).
5. Use of routine data
• Mortality data :
- Occupation is not reliably registered and coded on
the Belgian death certificate
- Only the last occupation
• Registers : occupation is mostly not registered
• Thus : standardization techniques are not in the course
EASOM Summerschool, Bari (IT), 1-9-2006
5. SPECIFIC CONTENT ISSUES
5.2. Major methodological issues
6. Cohort studies
• Relatively frequent :
rare exposure + historical personal hygiene records
--> retrospective / historical cohort studies
• Calculation of :
- Descriptive parameters
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Incidence risk
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Incidence rate (person-time)
- Associative parameter
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Relative risk
= I risk ratio
or I rate ratio
- Impact parameter
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Attributable risk (etiologic fraction)
EASOM Summerschool, Bari (IT), 1-9-2006
5. SPECIFIC CONTENT ISSUES
5.2. Major methodological issues
7. Case-control studies
• Nested within a cohort
• More efficient than analysis of the whole cohort
• Combination of
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Rare exposure (cohort)
Rare outcomes (case-control)
• For - common exposure
- dispersed groups (e.g. farmers)
Population-based case-control studies
EASOM Summerschool, Bari (IT), 1-9-2006
5. SPECIFIC CONTENT ISSUES
5.2. Major methodological issues
8. Prevalence studies
• Frequent use in practice
(description of a health problem)
• Mostly for non-fatal O. disorders (asthma, MSD, …)
• HWE is of concern
(prevalent cases = selected sample)
EASOM Summerschool, Bari (IT), 1-9-2006
STEPS IN CLUSTER INVESTIGATION
DISEASE TRACK
EXPOSURE T RACK
Orientation
disease
Step 1
Orientation
exposure
Orientation
association
Verification
disease
Step 2
Verification
exposure
Verification
association
Quantitative
analysis
disease
Step 3
Quantitative
analysis
exposure
Quantitative
analysis
association
Research
protocol
Specific
epidemiologic
study
EASOM Summerschool, Bari (IT), 1-9-2006