CASE STUDY FOR COHORT STUDY DESIGN

1. Wahengbam Bigyananda Meitei
MSc. Biostatistics & Demography 2015-17
Case Study for
Cohort Study Design
INTERNATIONAL INSTITUTE FOR
POPULATION SCIENCE

2. Contents
1. Framingham Heart Study
2. Nurses’ Health Study

3. Framingham Heart Study (FHS)
The Framingham Heart Study is a long-term.
Ongoing cardiovascular study.
Who in Cohort???
Residents of the town of Framingham, Massachusetts.
The study began in 1948 with 5,209 adult subjects from Framingham, and is now
on its third generation of participants.
It is a project of the National Heart, Lung, and Blood Institute, in collaboration
with (since 1971) Boston University.
The Framingham Heart Study is the origin of the term risk factor.

4. Framingham Heart Study (FHS)
Framingham Risk Score (FRS)
The 10-year cardiovascular risk of an individual can be estimated
with the easy to use Framingham Risk Score, including individuals without
known cardiovascular disease. The Framingham Risk Score is based on findings of
the Framingham Heart Study.
“High Normal Blood Pressure” increases risk of cardiovascular disease (high
normal blood pressure is called prehypertension in medicine; it is defined as a
systolic pressure of 120–139 mm Hg and/or a diastolic pressure of 80–89 mm Hg).

5. FHS Major findings
CHD
YEARS RESULTS
1960
Smoking + ve
Cholesterol & Elevated B.P. + ve
Exercise - ve
Obesity + ve
1970
Cholesterol & Elevated B.P. + ve
Postmenopausal + ve w.r.t Pre
Pshycological Factors + ve
1980 High levels of HDL cholesterol - ve
1990
Cholesterol & Elevated B.P. + ve
Enlarged Left Ventricle + ve
FRS is published, and correctly predicts 10-year risk of future
coronary heart disease (CHD) events. At 40 years of age, the
lifetime risk for CHD is 50% for men and 33% for women.

6. FHS Major findings
CHD 2000
Elevated blood pressure (Lifetime
risk 90%)
+ ve
Obesity (Lifetime risk approx. 50%) + ve
American Heart Association considers certain
genomic findings of the Framingham Heart Study
one of the top research achievements in cardiology
Some genes increase risk of atrial fibrillation.
Risk of poor memory is increased in middle aged
men and women if the parents had suffered from
dementia.

7. Nurses’ Health Study I (NHS I)
Established by Dr. Frank Speizer in 1976
Funded by the National Institutes of Health.
Also known as Original Nurses’ Health Study.
Primary motivation
To investigate the potential long term consequences of the use of oral
contraceptives, a potent drug that was being prescribed to hundreds of millions
of normal women.
Till date conducted 3 NHS

8. NHS I
Registered nurses were selected to be followed prospectively.
Why so???
Who & Who enrolled in Cohort
Married registered nurses who were aged 30 to 55 in 1976
California, Connecticut, Florida, Maryland, Massachusetts, Michigan, New
Jersey, New York, Ohio, Pennsylvania and Texas.
Why this 11 states???
Most populous states.
Nursing boards agreed to supply the study with their members’ names and
address.
Approximately 122,000 nurses out of the 170,000 mailed responded.

9. NHS I
Every two years cohort members receive a follow-up questionnaire, about diseases
and health-related topics including smoking, hormone use and menopausal status.
In 1980, the first food frequency questionnaire was collected. Then in 1984, 1986
and every four years since.
Questions related to quality-of-life were added in 1992 and repeated every four
years.
The nurses submitted 68,000 sets of toenail samples between the 1982 and 1984
questionnaires.
To identify potential biomarkers, such as hormone levels and genetic markers,
33,000 blood samples were collected in 1989-90 followed by second samples from
18,700 of these participants in 2000-01. These samples are stored and used in
case/control analyses.
Response rates to questionnaires are at 90% for each two-year cycle.

10. Nurses’ Health Study II (NHS II)
Established by Dr. Walter Willett and colleagues in 1989
Funded by the National Institutes of Health.
The primary motivation
To study oral contraceptives, diet and lifestyle risk factors in a
population younger than the original Nurses’ Health Study cohort.
Who are the younger population???
Younger generation who started using oral contraceptives during
adolescence and were thus maximally exposed during their early reproductive life.
Why NHS II???
Association with substantial increases in risk of breast cancer.
To collect detailed information on type of oral contraceptive used, which was not
obtained in the Nurses’ Health Study.

11. NHS II
Initial target population - Women between the ages of 25 and 42 years in 1989.
Original goal - To enroll 125,000 women.
Strategy - To do a single mailing inviting women to enroll and then only enroll the
most enthusiastic potential participants who would complete a single questionnaire
after one request, thus identifying those who would be most likely to continue
participation during the follow-up period.
Anticipated complications in follow-up with the target population
Names might change because of marriage
professional changes would be frequent, and
Women would have complicated, busy lives because of child-bearing.
Contacted States Nursing Boards to provide information on gender and date of
birth or age.
Initial mailing: California, Connecticut, Indiana, Iowa, Kentucky, Massachusetts,
Michigan, Missouri, New York, North Carolina, Ohio, Pennsylvania, South
Carolina and Texas.

12. NHS II
The overall response rate to the baseline mailing was approximately 24% .
After exclusions for incomplete forms and women who did not meet study
criteria, a total of 116,686 women remained in Nurses’ Health Study II.
Every two years, cohort members receive a follow-up questionnaire about
diseases and health-related topics including smoking, hormone use, pregnancy
history, menopausal status.
In 1991, the first food-frequency questionnaire was collected and subsequent
food-frequency questionnaires are administered at four-year intervals.
A two-page quality-of-life supplement was included in the first mailing of the
1993 and 1997 questionnaires.
Blood and urine samples from approximately 30,000 nurses were collected in the
late 1990′s.
Response rates to NHS II questionnaires are at 90% for each two-year cycle.

13. Nurses’ Health Study III (NHS III)
In 2010, Drs. Walter Willett, Janet Rich-Edwards, Stacey Missmer, and Jorge
Chavarro.
Collaborated with investigators at the Channing Laboratory and the Harvard
School of Public Health.
For the first time ever, the study is entirely web-based. Participants include
female LPN/LVNs and RNs, and it’s also open to nurses in Canada.
NHS III aims to be more representative of nurses’ diverse backgrounds. It will
closely look at health issues related to lifestyle, fertility/pregnancy, environment,
and nursing exposures.

14. Results of NHS given in Excel Sheet enclosed.
Sources :-
http://www.channing.harvard.edu/nhs/
https://www.framinghamheartstudy.org/