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Module 4 Overview
Context
Content Area: Interpretation of Epidemiological Evidence
Essential Question (Generic): Is the association causal?
Essential Question (Drug Abuse Specific): Is an association with drug abuse causal?
Enduring Epidemiological Understanding: Causation is only one explanation for finding
an association between an exposure and a disease. Because observational studies are
complicated by factors not controlled by the observer, other explanations must also be
considered.
Synopsis:
In Module 4, students explore the rationale and methods of interpreting epidemiological
studies. Students develop skills to assess possible explanations for an association
found in a study, with consideration of explanations of causality, chance, confounding,
reversed time order, and bias. Module 4 concludes with consideration of methods for
weighing the overall evidence for an association.
Lessons:
Lesson 4-1:
Lesson 4-2:
Lesson 4-3:
Lesson 4-4:
Lesson 4-5:
Lesson 4-6:
Lesson 4-7:
Introduction to Interpreting Associations
Causality
Chance
Bias
Confounding
Reverse Time Order
Weighing the Evidence
DrugEpi 4-6 Weighing the Evidence
Module 4 - Interpretation of Epidemiological Evidence
Lesson 4-6 Weighing the Evidence
Content
• Description of a legal case involving a stillbirth
and a mother who had used cocaine
• Consideration of the evidence for causality related to this case and of the role
that public opinion can also play
Big Ideas
• An association found in a single study or several studies with the same result
should consider five possible explanations for an association, including
causality, chance, bias, confounding, and reverse time order
• A judgment of causality may be made by considering several aspects of the
strength and quality of an entire body of scientific evidence about an
association
This project is supported by a Science Education Drug Abuse Partnership Award, Grant Number 1R24DA016357-01,
from the National Institute on Drug Abuse, National Institutes of Health.
DrugEpi 4-6 Weighing the Evidence
Where are we?
Essential Questions
Enduring Understandings
1.
How is this disease
distributed?
Health-related conditions and behaviors are not distributed uniformly
in a population. They have unique distributions that can be described
by how they are distributed in terms of person, place, and time.
2.
What hypotheses might
explain the distribution
of disease?
Clues for formulating hypotheses can be found by observing the way
a health-related condition or behavior is distributed in a population.
3.
Is there an association
between the
hypothesized cause and
the disease?
Causal hypotheses can be tested by observing exposures and
diseases of people as they go about their daily lives. Information
from these observational studies can be used to make and compare
rates and identify associations.
4.
Is the association
causal?
Causation is only one explanation for an association between an
exposure and a disease. Because observational studies are
complicated by factors not controlled by the observer, other
explanations also must be considered.
5.
What should be done
when preventable
causes of disease are
found?
Policy decisions are based on more than the scientific evidence.
Because of competing values - social, economic, ethical,
environmental, cultural, and political factors may also be considered.
DrugEpi 4-6 Weighing the Evidence
McKnight Case
“Regina McKnight is a 26-year-old native of Horry County, South
Carolina. She has an IQ that, prior to trial, was measured at 72,
i.e., “below average / borderline deficiency,” and attended
special education classes in high school. She was unable to
obtain a permanent job thereafter. Until 1998, Petitioner lived
with her mother, who helped her with day-to-day needs. In 1998,
however, Petitioner’s mother was killed by a hit and run driver.
Left without the support system on which she had relied, she
quickly spiraled downward, becoming homeless, addicted to
both cocaine and marijuana – and pregnant. Lacking access to
an adequate substance abuse treatment program, she was
unable to overcome her drug dependence.
(http://www.drugpolicy.org/docUploads/Petition_for_a_Writ_of_C
ertiorari.pdf)
DrugEpi 4-6 Weighing the Evidence
McKnight Case
“On May 15, 1999, McKnight was transported, in labor, to
Conway Hospital, where she delivered a stillborn girl. There
had been no prior indication that the fetus was in distress, and
it has never been suggested that McKnight intended to harm
the fetus. On the contrary, the attending nurse testified at trial
to having comforted McKnight, who was grief-stricken by the
stillbirth. As is common with distraught parents, Petitioner
asked to hold the stillborn baby and requested that
photographs of the baby be taken. She told hospital staff of
the name – “Mercedes” – that she had picked out for the baby.
She asked to be given a “memory certificate” with the baby’s
footprints and the bracelet that the baby had worn. She also
asked to see the hospital’s chaplain.
(http://www.drugpolicy.org/docUploads/Petition_for_a_Writ_of_
Certiorari.pdf)
DrugEpi 4-6 Weighing the Evidence
McKnight Case
“Within minutes of the stillbirth, however, hospital staff assumed
a second role. Following a carefully developed “protocol,” they
obtained a urine sample from McKnight, for drug testing. After
that screen indicated that cocaine was present, a nurse,
following the protocol, obtained McKnight’s signature on a form
entitled “Informed Consent for Drug Testing,” and collected a
second sample for “forensic” testing, with positive results
reported to the State Department of Social Services (“DSS”).
(http://www.drugpolicy.org/docUploads/Petition_for_a_Writ_of_
Certiorari.pdf)
DrugEpi 4-6 Weighing the Evidence
McKnight Case
“McKnight was arrested on October 7, 1999, and charged
under a statute proscribing “homicide by child abuse,” S.C.
Code § 16-3-85, which makes it a felony to “cause the death of
a child under the age of eleven while committing child abuse or
neglect,” if the death occurs “under circumstances manifesting
an extreme indifference to human life.” The law provides for a
prison sentence of twenty years to life. Id. § 16-3-85(C).
(http://www.drugpolicy.org/docUploads/Petition_for_a_Writ_of_
Certiorari.pdf)
DrugEpi 4-6 Weighing the Evidence
Background
How Drugs Cross the Placenta
http://www.merck.com/mmhe/sec22/ch259/ch259a.html
DrugEpi 4-6 Weighing the Evidence
Background
Cocaine
DrugEpi 4-6 Weighing the Evidence
Background
Stillbirth
DrugEpi 4-6 Weighing the Evidence
Background
Regina McKnight
DrugEpi 4-6 Weighing the Evidence
McKnight Case
Regina McKnight
Homicide by Child Abuse
DrugEpi 4-6 Weighing the Evidence
Demonstrating Causality
Beyond a Reasonable Doubt
The burden of proof required by the prosecution
in a criminal trial to obtain a guilty verdict.
DrugEpi 4-6 Weighing the Evidence
Review - Associations
Tied
Related
Associated
Linked
What do we mean when we say that
there is an association between two things?
Things that are associated
are linked in some way
that makes them turn up together.
DrugEpi 4-6 Weighing the Evidence
Interpreting Associations versus Judging Causality
On a study by study
basis, we try to
interpret associations
by looking at possible
explanations for those
associations
1. Causal
2. Chance
3. Bias
4. Confounding
5. Reverse
Time Order
As a body of scientific
knowledge accumulates, we consider all the
evidence that is available and try to judge
whether the weight of the evidence is
sufficient to demonstrate a causal association.
DrugEpi 4-6 Weighing the Evidence
Weighing the Evidence and Judging Causation
Sir Austin Bradford Hill
“The Environment and Disease:
Association or Causation?”
Proceedings of the Royal Society of Medicine
January 14, 1965
Relevance to the McKnight Case
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
Sir Austin Bradford Hill
“The Environment and Disease:
Association or Causation?”
Proceedings of the Royal Society of Medicine
January 14, 1965
Relevance to the McKnight Case
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
“In what circumstances can we pass
from this observed association
to a verdict of causation?”
DrugEpi 4-6 Weighing the Evidence
Causation: Epidemiological Versus Legal View
January 1994 - By Nancy A. Dreyer
THE PROCESS of determining causation and, in fact, the ultimate
need to determine causation is different in law and science. In law,
the goal of fairness seems to be paramount. Decisions are required,
no matter whether the true causes are known or understood. In
contrast, scientists have been described as "practitioners of a
discipline that seeks, but never finds, absolute truth" and as people
who use a "variety of criteria to evaluate data in conditions that
provide less than total certainty."(1)
If lawyers and courts knew how epidemiologists look at causation and
were aware of some of the methods used to provide scientific
inferences, perhaps they would recognize the case for accepting the
tentativeness of science and the scientific process. At a minimum,
this knowledge would enhance their facility to make fair and equitable
decisions.
“An Epidemiological View of Causation: How it Deffers from the Legal” at
http://www.pbs.org/wgbh/pages/frontline/implants/legal/ defensejournal2.html
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
“Here then are nine different viewpoints
from all of which we should study association
before we cry causation.”
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
Does the evidence support a verdict of causation?
1. Strength
2. Consistency
3. Specificity
4. Temporality
5. Biological Gradient
6. Plausibility
7. Coherence
8. Experiment
9. Analogy
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
Does the evidence support a verdict of causation?
1. Strength
What is the strength of the association between
prenatal cocaine exposure and stillbirth?
What is the strength of the association between
the exposure and the outcome?
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
Does the evidence support a verdict of causation?
2. Consistency
Has the association between prenatal cocaine exposure and stillbirth
been found consistently by different researchers, in different places,
using different study designs?
Has the association between the exposure and the outcome
been found consistently by different researchers, in different places,
using different study designs?
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
Does the evidence support a verdict of causation?
3. Specificity
Is prenatal cocaine exposure only associated with stillbirth
or is it associated with other outcomes as well?
Is the exposure only associated one outcome
or is it associated with other outcomes as well?
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
Does the evidence support a verdict of causation?
4. Temporality
Have studies established that
prenatal cocaine exposure precedes the stillbirth?
Have studies established that
the exposure precedes the outcome?
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
Does the evidence support a verdict of causation?
5. Biological Gradient
Has a biological gradient been demonstrated
between prenatal cocaine exposure and stillbirth?
Has a biological gradient been demonstrated
between the exposure and the outcome?
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
Does the evidence support a verdict of causation?
6. Plausibility
Is it biologically plausible
that prenatal cocaine exposure could cause stillbirth?
Is it biologically plausible
that the exposure could cause the outcome?
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
Does the evidence support a verdict of causation?
7. Coherence
Is the finding of an association
between prenatal cocaine exposure and stillbirth
coherent with our earlier knowledge?
Is the finding of an association
between the exposure and the outcome
coherent with our earlier knowledge?
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
Does the evidence support a verdict of causation?
8. Experimental
Is there experimental evidence,
in which stillbirths have been produced
by the prenatal administration of cocaine?
Is there experimental evidence,
in which the outcome have been produced
by the administration of exposure?
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
Does the evidence support a verdict of causation?
9. Analogy
Is the association between prenatal cocaine exposure and stillbirth
analogous to another association between an exposure and an outcome ?
Is the association between the exposure and the outcome
analogous to another association between an exposure and an outcome ?
DrugEpi 4-6 Weighing the Evidence
Back to the McKnight Case
Appeal
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
Amicus Curiae
Friend of the Court
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
Amicus Curiae
Friend of the Court
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
Amicus Curiae
Claim: Trial Counsel was ineffective for:
• failing to conduct an independent
investigation that would have revealed
readily accessible scientific information,
evidence, and potential experts who could
have testified regarding the etiology of
stillbirths, the state of scientific knowledge
regarding prenatal exposure to cocaine,
and the nature of addiction.
• failing to effectively cross examine the
state's experts, and to call witnesses that
were favorable to the defendant;
Friend of the Court
DrugEpi 4-6 Weighing the Evidence
• failing to adequately challenge the State’s
case for causation which was based
largely on misinformation, myth and
prejudice, rather than scientific fact.
Explaining Associations and Judging Causation
Assignment
Read the friend-of-the-court brief.
Identify the passages that address evidence for causality and the five
possible explanations for an association.
Identify the passages that address the five possible explanations.
Categorize, according to Hill’s cause / effect questions, the scientific
information, evidence, and expert testimony identified in the friends-ofthe-court brief that they think are good arguments for:
• A prosecution team trying to uphold the conviction
• A defense team trying to reverse the verdict against Regina McKnight
DrugEpi 4-6 Weighing the Evidence
END OF FIRST OF
TWO CLASSES
FOR Lesson 4.7
DrugEpi 4-6 Weighing the Evidence
Important Statement / Caveat
“It is important to note that each and every amicus curiae
is committed to reducing potential drug-related harms at
every reasonable opportunity. Thus, amici do not endorse
the non-medical use of drugs – including alcohol or
tobacco – during pregnancy, by either parent. Nor do
amici contend that there are no health risks associated
with cocaine (or other drug or alcohol) use during
pregnancy. Nonetheless, it is entirely consistent with
amici’s public health and ethical mandates to bring to this
Court’s attention the medical and scientific information that
is relevant to the case at hand.”
DrugEpi 4-6 Weighing the Evidence
Main Argument: Importance of Science
“… it is vital that convictions
be based on valid scientific evidence
rather than conjecture and misinformed popular opinion.”
DrugEpi 4-6 Weighing the Evidence
Influence of Popular Opinion
“For nearly two decades before trial,
the popular press was suffused with highly prejudicial
and often inaccurate information
about the effects of in utero cocaine exposure.”
DrugEpi 4-6 Weighing the Evidence
Science Versus Popular Opinion
“… valid scientific evidence …
(or) misinformed popular opinion.”
DrugEpi 4-6 Weighing the Evidence
Science Versus Popular Opinion
“… valid scientific evidence …
(or) misinformed popular opinion.”
DrugEpi 4-6 Weighing the Evidence
Influence of Circumstantial Evidence
“… circumstantial case of guilt
by simply producing evidence of a stillbirth,
and the fact of cocaine use
or any other unwise or unpopular behavior.”
DrugEpi 4-6 Weighing the Evidence
Precautions During Pregnancy
Avoid …
• Ingesting caffeine
• Gardening without gloves
• Changing a cat litter box
• Contact with anyone who is smoking
• Inhaling when handling household cleaning products
• Consuming unpasteurized cheese or undercooked meat
DrugEpi 4-6 Weighing the Evidence
A Weight of Evidence Review in JAMA
Deborah A. Frank et al.,
Growth, Development, and Behavior in Early Childhood Following Prenatal Cocaine Exposure:
A Systematic Review, 285 JAMA 1613 (2001)
DrugEpi 4-6 Weighing the Evidence
Three Criteria for Studies Included in JAMA Review
Detailed review was … restricted to studies that … met three criteria:
1.
samples were prospectively recruited;
DrugEpi 4-6 Weighing the Evidence
Three Criteria for Studies Included in JAMA Review
Detailed review was … restricted to studies that … met three criteria:
1.
samples were prospectively recruited;
2.
examiners of the children were masked to their cocaine exposure
status;
DrugEpi 4-6 Weighing the Evidence
Three Criteria for Studies Included in JAMA Review
Detailed review was … restricted to studies that … met three criteria:
1.
samples were prospectively recruited;
2.
examiners of the children were masked to their cocaine exposure
status;
3.
the cocaine exposed cohort did not include a substantial
proportion of children also exposed in utero to opiates,
amphetamines, or phecyclidine, or whose mothers were known to
be infected with the human immunodeficiency virus (HIV).”
DrugEpi 4-6 Weighing the Evidence
Conclusions of 2001 JAMA Review
Deborah A. Frank et al.,
Growth, Development, and Behavior in Early Childhood Following Prenatal Cocaine Exposure:
A Systematic Review, 285 JAMA 1613 (2001)
DrugEpi 4-6 Weighing the Evidence
Another Study Cited in the Brief
A Addis, ME Moretti, FA Syed, TR Einarson, G Koren
Fetal effects of cocaine:
An updated meta-analysis,
Reproductive Toxicology 2001; 15(4):341-369
What is a meta-analysis? A technique for combining
information from a number of studies in order to come up
with a summarization of the findings
The authors of Fetal Effects analyzed “all studies
employing methodologies suitable for proving cause and
effect relationships between cocaine and adverse
pregnancy outcomes.”
DrugEpi 4-6 Weighing the Evidence
Exclusions to Increase Rigor of Analysis
“Studies were excluded based on several criteria: because
they were case reports, editorials, letters, reviews or
commentaries, studies without fetal or pregnancy
outcomes, in vitro studies or placenta profusion, studies
with outcomes not within the scope of the meta-analysis,
studies without a control group and studies where cocaine
users had not been separated from users of other drugs.”
DrugEpi 4-6 Weighing the Evidence
Comparing Cocaine Use to Other Drug Use
“Fetal effects …” reports the following comparisons:
Comparison
Result
Poly-drug users versus non-drug users Effect of poly-drug use
Cocaine users versus users of drugs
other than cocaine
No difference
This suggests that there are other factors associated with
any drug use (not necessarily cocaine) that have a role in
causing the adverse developmental fetal effects
DrugEpi 4-6 Weighing the Evidence
Possible Confounders?
?
Cocaine or
other drug use
DrugEpi 4-6 Weighing the Evidence
Stillbirth or other
developmental
effect
Conclusions of Medical Community
“… it is the consensus of the medical community that the causes of
stillbirth, to a large extent, are not fully understood. ‘In the United
States, stillbirth accounts for a large proportion of all perinatal losses,
although its causes remain incompletely understood.’ At least ten
percent, but as many as fifty percent, of all stillbirths go entirely
unexplained. As a recent article, summarizing research available
before 2001, states: ‘In many cases it is difficult to be certain of the
etiology of stillbirth. First, many cases are unexplained, despite
intensive investigation of potential causes. Second, more than one
condition may contribute to stillbirth in an individual case.’ Moreover, ‘it
may not be possible to precisely determine which disorder was directly
responsible for the loss. Indeed, it is likely that some cases of stillbirth
are due to complications from multiple factors. Finally, conditions may
be associated with stillbirth without directly causing them.’"
DrugEpi 4-6 Weighing the Evidence
Conclusions of Medical Community
“… it is the consensus of the medical community that the causes
of stillbirth, to a large extent, are not fully understood. ‘In the
United States, stillbirth accounts for a large proportion of all perinatal
losses, although its causes remain incompletely understood.’ At least
ten percent, but as many as fifty percent, of all stillbirths go entirely
unexplained. As a recent article, summarizing research available
before 2001, states: ‘In many cases it is difficult to be certain of the
etiology of stillbirth. First, many cases are unexplained, despite
intensive investigation of potential causes. Second, more than one
condition may contribute to stillbirth in an individual case.’ Moreover, ‘it
may not be possible to precisely determine which disorder was directly
responsible for the loss. Indeed, it is likely that some cases of stillbirth
are due to complications from multiple factors. Finally, conditions may
be associated with stillbirth without directly causing them.’"
DrugEpi 4-6 Weighing the Evidence
Conclusions of Medical Community
“… it is the consensus of the medical community that the causes of
stillbirth, to a large extent, are not fully understood. ‘In the United
States, stillbirth accounts for a large proportion of all perinatal
losses, although its causes remain incompletely understood.’ At
least ten percent, but as many as fifty percent, of all stillbirths go
entirely unexplained. As a recent article, summarizing research
available before 2001, states: ‘In many cases it is difficult to be certain
of the etiology of stillbirth. First, many cases are unexplained, despite
intensive investigation of potential causes. Second, more than one
condition may contribute to stillbirth in an individual case.’ Moreover, ‘it
may not be possible to precisely determine which disorder was directly
responsible for the loss. Indeed, it is likely that some cases of stillbirth
are due to complications from multiple factors. Finally, conditions may
be associated with stillbirth without directly causing them.’"
DrugEpi 4-6 Weighing the Evidence
Conclusions of Medical Community
“… it is the consensus of the medical community that the causes of
stillbirth, to a large extent, are not fully understood. ‘In the United
States, stillbirth accounts for a large proportion of all perinatal losses,
although its causes remain incompletely understood.’ At least ten
percent, but as many as fifty percent, of all stillbirths go entirely
unexplained. As a recent article, summarizing research available
before 2001, states: ‘In many cases it is difficult to be certain of the
etiology of stillbirth. First, many cases are unexplained, despite
intensive investigation of potential causes. Second, more than one
condition may contribute to stillbirth in an individual case.’ Moreover, ‘it
may not be possible to precisely determine which disorder was directly
responsible for the loss. Indeed, it is likely that some cases of stillbirth
are due to complications from multiple factors. Finally, conditions may
be associated with stillbirth without directly causing them.’"
DrugEpi 4-6 Weighing the Evidence
Conclusions of Medical Community
“… it is the consensus of the medical community that the causes of
stillbirth, to a large extent, are not fully understood. ‘In the United
States, stillbirth accounts for a large proportion of all perinatal losses,
although its causes remain incompletely understood.’ At least ten
percent, but as many as fifty percent, of all stillbirths go entirely
unexplained. As a recent article, summarizing research available
before 2001, states: ‘In many cases it is difficult to be certain of the
etiology of stillbirth. First, many cases are unexplained, despite
intensive investigation of potential causes. Second, more than
one condition may contribute to stillbirth in an individual case.’
Moreover, ‘it may not be possible to precisely determine which
disorder was directly responsible for the loss. Indeed, it is likely
that some cases of stillbirth are due to complications from
multiple factors. Finally, conditions may be associated with stillbirth
without directly causing them.’"
DrugEpi 4-6 Weighing the Evidence
Conclusions of Medical Community
“… it is the consensus of the medical community that the causes of
stillbirth, to a large extent, are not fully understood. ‘In the United
States, stillbirth accounts for a large proportion of all perinatal losses,
although its causes remain incompletely understood.’ At least ten
percent, but as many as fifty percent, of all stillbirths go entirely
unexplained. As a recent article, summarizing research available
before 2001, states: ‘In many cases it is difficult to be certain of the
etiology of stillbirth. First, many cases are unexplained, despite
intensive investigation of potential causes. Second, more than one
condition may contribute to stillbirth in an individual case.’ Moreover, ‘it
may not be possible to precisely determine which disorder was directly
responsible for the loss. Indeed, it is likely that some cases of stillbirth
are due to complications from multiple factors. Finally, conditions
may be associated with stillbirth without directly causing them.’"
DrugEpi 4-6 Weighing the Evidence
Multi-Causality
”… it is scientifically inappropriate to declare fetal cocaine
exposure to be the sole or even primary cause of fetal death.”
A
L
X
DrugEpi 4-6 Weighing the Evidence
B
C
Health
Outcome
M
Y
Z
Multi-Causality
“… stillbirth could have resulted from any variety of natural
causes, including chorioamnionitis, funisitis, syphilis, meningitis,
pneumonia, sepsis, and chromosomal abnormalities.”
A
L
X
DrugEpi 4-6 Weighing the Evidence
B
C
Health
Outcome
M
Y
Z
Multi-Causality
“… at the time of trial, there were extensive literature and
studies establishing a wide variety of additional factors that
were associated, in varying degrees, with stillbirth.”
A
L
X
DrugEpi 4-6 Weighing the Evidence
B
C
Health
Outcome
M
Y
Z
Multi-Causality
Trial Counsel failed to raise this host of alternative explanations that
includes, but is not limited to, race and socioeconomic factors,
hypertension, diabetes, thrombophilia, infections, maternal smoking,
paternal smoking, paternal workplace exposure to ionizing radiation,
exposure to pain medications and of course, poverty.
A
L
X
DrugEpi 4-6 Weighing the Evidence
B
C
Health
Outcome
M
Y
Z
Explaining Associations and Judging Causation
Trial Counsel failed to raise this host of alternative explanations that includes, but is not
limited to, race and socioeconomic factors, hypertension, diabetes, thrombophilia,
infections, maternal smoking, paternal smoking, paternal workplace exposure to ionizing
radiation, exposure to pain medications and of course, poverty.
?
Cocaine
DrugEpi 4-6 Weighing the Evidence
Stillbirth
Explaining Associations and Judging Causation
Many findings once thought to be specific findings of in utero cocaine exposure
can be explained in whole or in part by other factors, including prenatal exposure
to tobacco, marijuana, or alcohol and the quality of the child’s environment.
?
Cocaine
DrugEpi 4-6 Weighing the Evidence
Stillbirth
Explaining Associations and Judging Causation
All scientific work is incomplete –
whether it be observational or experimental.
All scientific work is liable to be upset
or modified by advancing knowledge.
That does not confer upon us the freedom to ignore the
knowledge we already have, or to postpone the action
that it appears to demand at a given time.
DrugEpi 4-6 Weighing the Evidence
Aftermath
What has happened to Regina McKnight?
• The appeal was successful so a new trial was allowed.
• McKnight plead guilty to a lower charge (manslaughter)
and was freed for sufficient sentence already served)
• She has three other children and said that she wanted
to be with them again and that she had learned a lot
about herself when she was in jail.
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
Send a Message
Deterrent
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
Epidemiology
... the study of the distribution and
determinants of health-related
states or events in specified
populations and the application of
this study to the control of health
problems.
Leon Gordis, Epidemiology, 3rd Edition, Elsevier Saunders, 2004.
DrugEpi 4-6 Weighing the Evidence
Explaining Associations and Judging Causation
DrugEpi 4-6 Weighing the Evidence
Re-Cap
Big Ideas in this Lesson (4-7)
•
•
An association found in a single
study or several studies with the same result should
consider five possible explanations for an association,
including causality, chance, bias, confounding, and
reverse time order
A judgment of causality may be made by considering
several aspects of the strength and quality of an entire
body of scientific evidence about an association
This project is supported by a Science Education Drug Abuse Partnership Award, Grant Number 1R24DA016357-01,
from the National Institute on Drug Abuse, National Institutes of Health.
DrugEpi 4-6 Weighing the Evidence
Next Lesson
Policy: Needle Exchange Programs
DrugEpi 4-6 Weighing the Evidence