1. Study Designs Group Work

2. Epidemiological Studies
Descriptive studies
Analytic studies
Intervention studies
Observation Studies
Individuals
Population
Experimental studies (clinical trials)
-Case Control Studies
-Cohort studies
-Case Report
-Case series
-Cross Section Studies
Correlation Studies

3. The Five W’s of Journalism / Epidemiology
What
Who
Where
When
Why / How
Clinical
Person
Place
Time
Cause,
mode of
transmission, risk factors
Descriptive Epidemiology
(Distribution)
Analytic
Epidemiology
(Determinants)

4. DESCRIPTIVE STUDIES Advantages: They use already available data
They are less expensive and less time consuming
They describe the pattern of disease occurrence
They formulate research hypothesis

5. I. Correlation or Ecological Studies
Based on aggregate measures of exposure and outcome from several populations.
The population is the unit of observation available for study.

7. II. Case report and case series
The individual is the unit of observation.
They describe the experience of a single patient or a small number of patients with a similar diagnosis reflecting unusual features of a disease.
They help in:
formulation of a hypothesis on etiological association
represent the first clues in identification of new disease or epidemic.

8. III. Cross sectional surveys
Collection of data on several individuals at “one point” in time.
Determines prevalence at a point in time
Therefore, CS is a prevalence study
The exposure and disease status are assessed simultaneously among individuals in a well defined population.
Snapshot in time

9. Cross Sectional Studies
Disease
Total
Present
Absent
Exposure
present a b
a+b
absent c d
c+d
a +c
b+d N

10. Design of a C-S Study

11. CASE-CONTROL STUDIES Disease Exposure a +c b+d Total Present Absent a
c+d
a +c
b+d N

12. Case-Control Studies – Timing
Exposure
Disease ?
Exposed
Unexposed
Yes (case)
No (control)
In a typical case-control study, the investigator begins the investigation after disease has occurred. The investigator enrolls cases (who have the disease), a group of people who do not have the disease (“controls”). The investigator then collects information about prior exposures from the cases and controls. In this way, case-control studies begin with disease and move “backwards” to exposure.
Investigator

13. Strengths: Suitable for diseases of long latency period
Quick and inexpensive (as compared to other analytic studies)
3. Suitable for rare diseases
4. Can examine multiple etiologic factors for a single outcome.
5. Requires fewer subjects at entry
6. Few ethical problems

14. Case-Control – 2-by-2 Table
Exposed a
Unexposed c V1
Control b d V2
While technically the odds ratio is the ratio of odds (a/c) divided by (b/d/), it is much easier to calculate it (and to remember the formula) as ad/bc.
Odds Ratio = (a/c) / (b/d) = ad / bc

15. COHORT STUDIES Disease Total Present Absent Exposure present a b a+b
c+d
a +c
b+d N

16. Strengths:
1. Establish the temporal relationship between exposure and disease
2. Useful for rare exposures
3. Examine multiple outcomes of single exposure
4. Allows direct measurement of incidence of the disease among exposed and unexposed groups.

17. Analysis Incidence among exposed
Relative Risk (RR)=
Incidence among non-exposed
a / a+b
RR =
c/ c+d

18. Types of Cohort Studies:
1. Retrospective Cohort Study
2. Prospective Cohort Study
3. Ambidirectional Cohort Study

19. INTERVENTIONAL STUDIES “CLINICAL TRIALS” “Experimental Studies”

20. Investigator
Determines
Exposure Status

21. “CLINICAL TRIALS” Strengths:
1. The gold standard of epidemiological studies.
2. Detect mild to moderate differences (10-20%)
3. Can control many confounding factors
4. Can demonstrate the temporal relationship with the highest degree of confidence
5. Randomized trial can yield the strongest and most direct epidemiological evidence to judge on causal association

22. Randomized Clinical Trial
Design of a
Randomized Clinical Trial

23. Selection of Subjects: Stratified Randomization

24. Relative risk is the measure of association in clinical trials.
Analysis
Relative risk is the measure of association in clinical trials.

25. Group 1
In a study to determine the role of coffee consumption on risk of development of ovarian cancer, 188 patients with epithelial ovarian cancer were compared with 280 hospital controls and 259 health controls from the general population.
The results were as follows:

26. Coffee drinking
Cases
Hospital Controls
Population Controls
Total
Yes
177
249
233
659 No 11 31 26 68
188
280
259
727

27. What is the design of this study?
Calculate the measure(s) of association
In your opinion, why they used two control groups?

28. Group 2
A research team wishes to investigate a possible association between smokless tobacco and oral lesions among professional football players. At spring training camp, they ask each player about current and past use of smokeless tobacco, cigarette and alcohol, and a dentist notes the type and extent of the lesions in the mouth.

29. 80 30 110 2 34 36 82 64 146 Mouth lesions No Lesions Total
Smokless Tobacco
Users 80 30
110
Non Users 2 34 36 82 64
146

30. What is the design of this study?
Mention the single most important limitation of this study design.
Calculate the measure of morbidity in the entire group.

31. Group 3
100 individuals were inoculated with a vaccine against certain infectious disease, and 100 indistinguishable from the first group received a placebo.
During a subsequent epidemic, although the two groups had similar exposure, 20 of the vaccinated group, and 50 of the un-vaccinated group developed the disease.

32. What is the design of this study
Is the vaccine effective?
Calculate vaccine efficacy.

33. Group 4
An investigator wishes to study the relationship between bladder cancer and frozen yogurt. He gets cases of bladder cancer from the cancer registry and a control population of patients attending the urology clinic for reasons other than bladder cancer. He then interviews each patient to find out if they consume frozen yogurt.
Since smoking has also been shown to be associated with bladder cancer, he also classified cases and controls as either smokers or non-smokers. The results of the study are shown in the following table.

34. 150 100 50 200 200 100 Smokers cases control Yogurt Use Users
Non users 50
200
Non Smokers
cases
control
Yogurt Use
Users
200
100
Non users

35. What is the design of this epidemiological study?
Calculate the measure of association among smokers, non smokers, and the whole group.
What do we call smoking in this example

36. Group 5
To assess the relationship between hypothyroidism and myocardial infarction, 1,000 women aged >55 years with hypothyroidism were compared with 3,000 women aged >55 years free from hypothyroidism.
All had no past history of myocardial infarction.
After a follow up period of 5 years, 40 females with subclinical hypothyroidism developed myocardial infarction (MI) and another 30 females with no evidence of subclinical hypothyroidism also developed MI.

37. Construct the suitable table
What is the design of this study?
Calculate the measure of association between Hypothyroidism and MI
Interpret the result.