Transcript Review Session.ppt

Review Session
November 29, 2010
Questions Study Design - 1
• Questionnaires were mailed to every 10th person listed
in city telephone directory. Each person was asked to
list age, sex, smoking habits, and respiratory
symptoms, during the preceding seven days. About
20% of questionnaires were completed and returned.
About 10% of respondents reported having upper
respiratory infections.
Cross sectional/prevalence and/ prevalence
Questions Study Design - 2
• 1500 employees of a major aircraft company were
initially examined in 1951 and were classified by
diagnostic criteria for coronary artery disease (CAD).
Later New cases of CAD have been identified by
examinations every three years and through death
certificates. Incidence rate in different subgroups have
been computed
Subgroups from 1951 could be could be smokers or
non smokers; obese and non obese,
• Prospective cohort study
Questions Study Design - 3
• A 39 year old woman presents with a mild sore
throat, fever, malaise, and headache, and is
treated with penicillin for presumed streptococcal
infection. She returns in a week with
hypertension, fever, rash, and abdominal pain.
She responds favorably to chloramphenicol after
a diagnosis of rocky mountain spotted fever
• Case report
Questions Study Design - 4
• A random sample of middle age sedentary adults
was selected from four survey/census tracts, and
each person was examined for coronary artery
disease (CAD). All persons without disease were
randomly assigned to either a two year program
of aerobic exercise or a two year arthritis
prevention non aerobic exercise program. Both
groups were observed semi annually for
incidence of CAD.
• Randomized control trial
Questions Study Design - 5
• 50 patients of thyroid cancer are identified and
surveyed by patient interviews to identify
previous radiation exposure
• Note that there is No control group
• Case series
Questions Study Design - 6
• Patients admitted for carcinoma of stomach and
patients without a diagnosis of cancer are interviewed
about their chewing tobacco history to assess possible
association of chewing tobacco and gastric cancer
Note that there is a control group without disease
Hence Case control design
• Case control study
Questions Study Design - 7
• Data on median income for households in census tracts
within a large metropolitan county in USA were obtained
from census bureau current population survey. Air
pollution levels were measured in these same census
tracts during a period f one month. The data were
analyzed using a geographic information system (GIS) to
produce maps showing pollution and income levels by
census tracts
• Note it is looking at group data (air pollution and income)
• Ecologic study design/ correlation
Questions Study Design - 8
• In a village 100 Neonatal tetanus cases were
compared with 300 neonates without history
of neonatal tetanus (controls); 17% of cases
gave history of butter application to umbilical
cord; compared to 7% of controls.
• a) State a study design
• b) Make a 2x2 table and calculate Odds Ratio.
How to draw 2x2 table
Exposure
Butter
applied
Butter not applied
Total
Disease +
Or Cases
Neonatal Tetanus
Disease Controls
Healthy neonates
How to draw 2x2 table
Exposure
Disease +
Or Cases
Neonatal Tetanus
Disease Controls
Healthy neonates
Butter
applied
Butter not applied
Total
100
300
How to draw 2x2 table
Exposure
Butter
applied
Butter not applied
Total
Disease +
Or Cases
Neonatal Tetanus
17
Disease Controls
Healthy neonates
(7/100 x300)
Can u fill
=21
?
100
300
How to draw 2x2 table
Exposure
Butter
applied
Butter not applied
Total
Disease +
Or Cases
Neonatal Tetanus
17
Disease Controls
Healthy neonates
(7/100 x300)
100-17
= 83
=21
300-21=
279
100
300
How to draw 2x2 table
Exposure
Disease +
Or Cases
Neonatal Tetanus
Disease Controls
Healthy neonates
Butter
applied
Butter not applied
17
21
83
279
Total
100
300
How to draw 2x2 table
Exposure
Butter
applied
Butter not applied
Total
Disease +
Or Cases
Neonatal Tetanus
Disease Controls
Healthy neonates
(a)17
(b)21
( c)83
(d)279
100
300
Odds Ratio
• Done in Case Control Study
• Also in Cross Sectional Study
• ad/bc
• =(17x279) / 21x83
• = 4743/1743
Question
• In a village 100 Neonatal tetanus cases were
compared with 300 neonates without history
of neonatal tetanus (controls); 6% of cases
were delivered by skilled birth attendants
compared 19% of controls. Make a 2x2 table
and calculate Odds Ratio.
• a) Make a 2x2 table and calculate Odds Ratio.
• b) Interpret Odds Ratio
Question- Relative Risk
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A cohort study regarding exposure to animal hides, followed 400 exposed and 400 non
exposed subjects for five years to observe the development of dermatitis. Of the
exposed 180 developed dermatitis and those who were unexposed 50 developed
dermatitis. Calculate the Relative Risk and interpret
ANM HID+
ANM HID-
DERM+
180
50
180/400= .45
50/400-= .125
RR= .45/.125=3.6
Incidence
DERM 220
350
TOT
400
400
How to draw 2x2 table
Exposure
Disease +
Or Cases
Dermatitis
Disease No Dermatitis
Total
Animal
Hides +
400
Animal
Hides -
400
How to draw 2x2 table
Exposure
Disease +
Or Cases
Dermatitis
Disease No Dermatitis
Total
Animal
Hides +
180
(a)
220
(b)
400
Animal
Hides -
50
©
350
(d)
400
Relative Risk
• RR = a/ (a+b)
b/(b+d)
Calculate
Explain the design of case control study
What measure of association is used in a case control study
ODDS RATIO