Lesson 4: Scientific Method
Estimated Time: 35 minutes
Teachers: Divide the class into small groups and respond to these
questions, then have group members report their responses to the class.
Before starting any investigation, it is
good to find background facts on the problem.
Small
Group Discussion
How could you learn more about
birth defects? Where could you go to find more facts on birth
defects? Who could you talk to for this information?
Places to learn more could include the
internet, encyclopedias, books, and magazines. People to talk to could
include a parent who has a child with a birth defect, people with spina
bifida, workers from the March of Dimes or a public health department, or
doctors and nurses who treat people with spina bifida.
Small
Group Discussion
Suppose you are a scientist and you
have been told to go to Brownsville, Texas to find out what is causing the
cases of anencephaly. What do you need to do before you go?
What do you need to bring?
Gather study supplies like a laptop
computer, lab equipment, a map and list of places to go, and a notebook. You
should also prepare a list of questions to ask the women who have had a baby
with the birth defect. You will also have to make reservations for the trip
and make a plan for who to meet and what to do once you arrive at the study
area.
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Step 2) Show that an
outbreak exists
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RATE. The number of cases in a
population during a certain time. |
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An outbreak occurs when there are more
cases of a certain disease than expected. To know if an outbreak exists,
we need to know if the number of cases is above what is expected. In the
U.S., the rate of NTDs is 1 per 1000 babies. This means that on
average for every 1,000 babies born, one is born with an NTD.
Individual
Activity
About 6,000 babies are born per year in
Cameron County. If the rate of neural tube defects in the U.S. is 1
per 1,000 births, how many of the 6,000 babies born in Cameron County in a
year would you expect to have an NTD?
6,000 babies X 1 NTD = 6 NTD-affected
births/year (expected)
1,000 births
In real life, six babies were born
with anencephaly in Brownsville within 6 weeks in 1991.
If these rates continued, how many babies would you expect to
be born with anencephaly in Cameron County in a whole year?
6 NTDs X 52 weeks
= 52 NTD-affected births/year (projected)
6 weeks 1 year
Small
Group Discussion
Compare
the expected rate from U.S. averages to the projected rate if the rates in
Cameron County continued. Do you think this problem should be
investigated? Give at least two reasons this problem should be
studied.
To gain more knowledge about
what could cause NTDs
To prevent more birth defects
from happening in the area
To find out what caused the
increase in NTDs
What is the rate of NTDs in your state?
You could check health department reports, birth and death records, and
hospital records. Another way to find out would be to check
out your State Birth Defects Surveillance System. Go
here and open Appendix C to find a state contact. Pages 6-14
list the contacts by state.
Check out the
Texas Department of Health Birth Defects Monitoring Division's Web site
for current information. Use the back button on your browser to
return to this lesson.
A third step is to make sure the cases
of anencephaly were true cases. Sometimes
laboratories make mistakes or new doctors count cases in a different way.
When this happens, it can seem like an outbreak when there really aren't
more cases than normal. Anencephaly is easy to notice because it is
obvious when a baby doesn't have a skull and part or all of its brain.
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Step 4) Define and find
all cases
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CASE DEFINITION. A way to
describe who has the health problem by identifying what
happened, where it happened, and when it happened. For
example, if several students got sick after eating lunch at
school, the case definition would include only those
students at that particular school who threw up at least 3
times on May 1st and 2nd. In the NTD study in Cameron
County, researchers defined a case as -- anencephaly
diagnosed in babies born in Cameron County during 1986-1991. |
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The researchers wanted to look for NTD cases before 1991
to see if the current rates were higher than normal. First, they
needed a case definition. This case definition would
help them decide who to study. They decided to include all babies
whose NTDs were noted in medical records from 1986 to 1991 in Cameron
County. Then they searched records and counted the cases they found.
Small
Group Discussion
If you were trying to find all the cases of anencephaly, where would
you look for this info? (Hospitals, birth and death certificates,
health departments, mothers, laboratories, death records, doctors' files,
clinic records, district health record)
Medical records at hospitals, and at a local spina
bifida clinic were studied to find the prevalence of NTDs in Cameron County.
The rate of NTDs from 1986 until 1989 was 1.5 per 1,000 births. In
1990 and 1991 the rate was 2.7 per 1,000 births. All of these numbers
are higher than the national average of 1 case per 1,000 births.
Researchers have found that Hispanics have a higher rate of births with an
NTD than the general U.S. population, but they do not know why.
Because Cameron County has a large Hispanic population, we can expect the
rate for Cameron County to be higher than the U.S. rate. In 1990 and
1991, the rate of 2.7/1000 is about three times higher than the average rate
in the U.S.
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Step 5) Describe and line up the data
in terms of time, place, and person
The researchers gathered data about all the births.
Follow the link to find a
graph of all known NTD cases in
Cameron County from 1980 to 1992. Also, click to find a
graph of anencephaly cases from 1985 to 1996.
Small
Group Activity
Have the students interpret the graphs (possibly on an
overhead) and discuss what they think may have happened.
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Step 6) Make hypotheses (educated
guesses)
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Step 7) Test hypotheses
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Step 8) Refine hypotheses and carry
out more studies
When these cases occurred in Cameron County in 1991,
little was known about the cause of NTDs like anencephaly. It was
known that in the United States NTDs are most common among Hispanics and
least common among African Americans. The birth defects are also
more common in poorer families. Researchers from the CDC wanted to
know what was causing the NTDs. If there was a problem that was
causing these deaths, they wanted to find it so that they could stop the
problem. Community members thought the birth defect problems could
be caused by pollution from pesticide use and the growing assembly plant
industries along the Mexico/U.S. border. The scientists used all of
the information they gathered to make educated guesses (they made
hypotheses) and investigated each of these factors (they tested
hypotheses). Then, they decided to:
1) Conduct a case control study to define risk
factors of the parents of cases and controls
2) Conduct lab testing for nutrition and environmental factors
3) Test air, soil, water, and pesticides
One part of the study was to conduct a
Case-Control Investigation.
CASE-CONTROL STUDY. An type of
retrospective study that uses cases (health problem) and compares them
with controls (without the health problem) to find out what may have
caused the problem. |
Twenty-eight babies who died from anencephaly from
1989 to 1991 were found from the birth and hospital records. The
mothers of these babies were called the case mothers.
Then 26 mothers who had normal babies born during the same 2 years were
chosen. These mothers were called control mothers.
Since this type of study looks at a problem that already happened it is
called a retrospective study.
Epidemiologists interviewed the mothers of these babies
in either English or Spanish. Both the case mothers and control
mothers were asked 300 questions about their lives 6 months before pregnancy
and during pregnancy. Some of the questions were about where
they lived, where they worked, what they ate, how often they visited a
doctor, what type of work they did, where they got their drinking water, and
if they had air conditioning. The mothers' blood and urine were tested
for chemicals that may have been in their bodies and could harm the baby.
Drinking water, surface water, air, and soil were tested. Records were
checked for past pesticide use (chemical spraying for bugs) near the
mothers' homes. The scientists made a map showing where the case
mothers and control mothers lived to see if there were any major differences
between the two groups.
Click here to see map.
Note: this type of map is new for many students. Point
out the importance of reading the title and key. The lines are
streets, the triangular and circular symbols represent the homes of case
mothers and control mothers in the study, and the Rio Grande River at the
bottom separates Texas from Mexico. Ask the students what they learned
from the map. This was an actual map used by researchers. They
found no real difference between the resident areas of case mothers and
control mothers.
When all of the interviews were finished and the data
were analyzed, no real differences were found between the cases and
controls. Mothers of both the normal babies and the babies with the TD
lived in similar homes and locations, ate about the same types and amounts
of foods, worked in the same types of jobs, received about the same amount
of prenatal (before birth) care, etc. Tests of air, soil, water, and for
chemicals found that everything was normal. The one thing that they
did find was that women who didn't finish high school were more than twice
as likely to have a baby with an NTD than women who had graduated.
Small
Group Discussion
Discuss possible reasons more mothers who didn't finish high school had
babies with NTDs.
Education could make a difference because women who
finish high school may have learned more about health and may be older and
better prepared for pregnancy. Education could allow people to have
better jobs, earn more money, and have better homes, nutrition, and medical
care.
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Step 9) Begin control and
prevention measures
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Step 10) Share findings
After the study, scientists said that:
1) Women who have already had an affected
pregnancy should take folic acid. More research about folic acid
should be done.
2) The state needed a more complete system to keep
track of all the NTD cases in the state and especially along the border.
(In 1993, Texas Department of Health began closely tracking all babies born
with NTDs along the border).
3) More studies should be done to look for causes
of birth defects in this high-risk area.
4) The air should be checked for toxins (chemical
poisons) on an ongoing basis.
See linked articles
about Texas birth defects surveillance.
After these studies were finished, the scientists still
didn't find an exact cause of these birth defects occurring along the
border. Some people living in the area think that pollution from
factories across the Mexican border may have caused the problem, but there
has been no evidence to show that to be the cause. Even with studies
going on now we still don't know exactly what caused the increased numbers
of these birth defects. Often birth defect clusters are unsolved.
Maybe you can think of birth defect clusters that you'd like to solve
someday.
Link to
Lesson 5: Folic Acid Epidemiology Studies
Date: September 6, 2006
Content source: National Center on Birth Defects and Developmental
Disabilities
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