Transcript EMF for Harlem Children Society

Harlem Children Society – Mentoring Lecture
July 27, 2006
Scientific Methodology for Assessing
Public Health Issues: A Case Study of
EMF
William H. Bailey, Ph.D.
Principal Scientist
“The Scientific Method”
The scientific method is the process by
which scientists,
collectively and over time,
endeavor to construct an accurate
representation of the world.
Steps in the Scientific Method
• Observation and description of a
phenomena
• Formulation of an hypothesis to explain
the phenomena
• Use of the hypothesis to predict the
existence of other phenomena
• Experimental tests of the predictions by
several independent experimenters and
properly performed experiments
Flow diagram describing the
scientific method
The Scientific Method (con’t)
1. Observe some aspect of the universe
2. Invent a tentative description, called a hypothesis, that is
consistent with what you have observed
3. Use the hypothesis to make predictions
4. Test those predictions by experiments or further
observations and modify the hypothesis in the light of your
results
5. Repeat steps 3 and 4 until there are no discrepancies
between theory and experiment and/or observation
STEPS 4 and 5 REQUIRE INTERPRETATION
Origin and modification of the EMF
Hypothesis
Observation
It seems as if children with cancer live near polemounted transformers on utility distribution lines
Hypothesis
Something about distribution lines increases the risk of
cancer in children
Prediction
Children who live near power lines will have a higher
rate of cancer than those who do not
Tests
Expose laboratory animals and cells. Compare
exposures of cancer cases and controls
What is there about power lines that
we can measure and study?
• Wertheimer & Leeper (1979) considered 3
exposures
– PCBs in pole transformers
– EMFs from distribution lines and other
electrical facilities
– Air pollution
(because they observed that large 3-phase
distribution lines are frequently located located along
heavily traveled roads)
Power Lines and EMF
• Power lines produce electric and
magnetic fields (EMF)
– Electricity produces EMF that changes
direction and intensity 60 times per second –
a frequency of 60 Hertz (Hz)
– EMF are produced by other sources that
surround us in our daily lives
EMF
Spectrum
Source: NIEHS, 2002
Electric Fields
• Electric fields result from voltages
• Measured in units of volts per meter (V/m)
or kilovolts per meter (kV/m)
– 1000 V = 1 kV
• Shielded from objects such as trees,
shrubs, and walls
• Strength diminishes as you move away
from the source
Magnetic Fields
• Magnetic fields result from current flow
• Measured in gauss (G) or milligauss (mG)
or microtesla (µT)
– 1000 mG = 1G = 100 µT
• Not shielded from objects such as trees,
shrubs, walls
• Strength diminishes as you move away
from the source
Source: NIEHS, 2002
Magnetic Fields in Everyday Life
Modifying the Hypothesis
Developments in Science
• Evidence stronger for magnetic than
electric fields
• Methods to calculate fields from power
lines
• Personal ‘dosimeters’ developed
• Studies show no consistent link with
childhood brain cancer
Personal Dosimeter
How Do Scientists Evaluate
Potential Risks of Exposure?
• Epidemiologic observations
• Laboratory studies in animals
• Laboratory studies in cells and tissue
Epidemiology
•Compares characteristics of people
with and without a disease
•Statistical associations between
people and exposure
•Observational, not experimental
•Strength: Studies people
Epidemiology
The study of factors that cause
disease or influence health in
the human population
• Observational research
• Includes scientific method for assessing
causality
An Example of Association
Gambling
Cancer
•
Cancer occurrence was found to be
greater people who gamble than in
comparison populations
•
Gambling is associated with cancer
The Association is Indirect
Gambling
Cancer
Alcohol/Smoking
Consumption
In this example, alcohol consumption and
smoking are confounding factors
Interpretation of Relative Risk (RR)
• If disease rate, or risk, is the same in
both groups, then RR will be 1.0
– Interpreted as “no association”
• If disease rate (risk) is greater in exposed
population, then RR will be > 1
– Interpreted as a positive association with the
disease
Cases
Controls
Case-Control Study Design
Base Population
Disease
Exposed (A)
Non-exposed (C)
No Disease
Exposed (B)
Non-exposed (D)
Association of Childhood Leukemia with 48-hr
Personal Exposure
1.2
Odds Ratio
1.0
0.8
0.6
0.4
0.2
0.0
<0.08
0.08-<0.15
0.15-<0.27
Magnetic Field (µT)
Source: McBride et al. 1999
0.27-1.61
Interpreting Data
Are observed results due do
Confounding?
Chance?
Bias?
Individual Characteristics That Modify
the Effect of Environmental Factors
Gender
Genetic factors
Nutrition
Disease
Age
Physical condition
Behavior
Judging Whether
an Association is Causal
•
•
•
•
•
•
Strength - Is it strong or weak?
Consistency
Dose- response
Correct timing
Biological plausibility
Experimental evidence
Hundreds (and Hundreds) of Studies
Conducted in Past 30 Years
• Epidemiology (Observational) Studies
– Some residential studies have reported
statistical associations between magnetic
field exposure and some types of cancer
– This prompted additional research
– All studies are not equal!
• The larger and more reliable studies have not
found these associations
Polling Prediction Error in 1948
Presidential Election
Examples of Scientific Method
‘Failures’ - Epidemiology
• Prediction of Dewey win over Truman in
1948 US presidential election
• Association between use of VDTs and
miscarriage in California
• Association of childhood leukemia with
EMF and selection/response bias
• Non-failure – Magnesium sulfate and
heart attack
Experimental Studies of EMF
Exposure and Health
Laboratory (animals)
Laboratory
(cells and tissues)
Experimental science —
control over relevant
variables
Typical Experimental DesignSubjects randomly assigned to:
• Exposed Group
–
–
–
–
–
–
–
EMF
Temperature
Humidity
Genetics
Age
History
Health status
• Control Group
=
=
=
=
=
=
–
–
–
–
–
–
–
No EMF
Temperature
Humidity
Genetics
Age
History
Health status
Examples of Scientific Method
‘Failures’ – Experimental studies
•
•
•
•
•
Mortality of young rats and mice
Damage to DNA
Calcium uptake by white blood cells
Melatonin hormone levels in rats
Non-failure - Stress-induced heart
damage
• Malformations in chicken eggs
• Metabolic changes in marine cells
Hundreds (and Hundreds) of Studies
Conducted in Past 30 Years (con’t)
• Experimental Studies
– Laboratory animals exposed to high levels of
magnetic fields for their entire lifespan had
no increase in cancer overall, or types of
cancer statistically linked with EMF sources
in some epidemiology studies
– EMF does not damage cells like known
cancer-causing agents
• Weight-of-the-Evidence Reviews
Weight-of-the-Evidence
• The data must present a logically
consistent and coherent picture
• Underlying concepts
– Things that cause cancer in animals tend to
cause cancer in humans
– Cells exposed to cancer-causing agents
show typical changes
– “The dose makes the poison”
– Systematic methods must be used to limit
misconceptions
Interpreting Results
• All studies are not equal
• Association is not causation
• Research is evaluated
in context
Science, Slogans and Civic Duty
– Donald N. Langenberg
“When the time comes to move from debate to
action, action is shaped by the perceptions and
values of the leaders of the debate. Sometimes
these perceptions and values reflect the relevant
body of scientific knowledge, and sometimes
they do not.”
Science, 252:361-363, 1991
Scientific Reviews of EMF Research
by National/International
Organizations
•
•
•
•
Large panels, balanced composition
Experts in multiple disciplines
Defined methodology
Conclusions represent a consensus
Other Scientific Reviews
Potential issues as to:
• Overweighting of extreme views
• ‘Missing’ expertise in one or more
disciplines
• Ad hoc approach and unfamiliarity with
risk assessment
• Conclusions may be biased towards views
of one or two persons
International and National
Scientific Review Groups
• National Institute of Environmental Health
Sciences (NIEHS)
• U.S. National Academy of Sciences (NAS)
• International Agency for Research in
Cancer (IARC)
• National Radiological Protection Board of
Great Britain (NRPB)
• Health Council of the Netherlands (HCN)
• World Health Organization (WHO)
Federal-Provincial-Territorial Radiation Protection
Committee- Canada (2005)
• Established to support government radiation
protection agencies in Canada
• Review of epidemiology and laboratory
research regarding 60-Hz EMF
• Conclusion
– “Adverse health effects from exposure to power-frequency
EMFs, at levels normally encountered in homes, schools and
offices, have not been established.”
– “Since there is no conclusive evidence that exposure to EMFs
at levels normally found in Canadian living and working
environments is harmful, FPTRCP is of the opinion that
moderate measures and participation in the process of
acquiring new knowledge are sufficient.”
What are the Views of
Scientific Review Panels?
• They agree that there is little evidence
suggesting that EMF is associated with
adverse health effects
• They believe that there is some
epidemiological evidence that EMF at high
exposures is linked to childhood leukemia
• They agree that the laboratory data does
not support a link between EMF and any
adverse health effect, including leukemia
• They have not concluded that EMF is
known to cause any disease