Question

In a study concerning the relationship between the use of exogenous estrogens and subsequent risk of breast cancer, a sample of 1000 pre-menopausal women was followed for 8 years. The results are presented in the table below.

	Breast Cancer
Estrogen Therapy	Present	Absent	Total
+	300	200	500
-	100	400	500
Total	400	600	1000

1.What kind of study is this?

1. cross-sectional
2. ecological
3. case-control
4. cohort

2.Is this study prospective or retrospective?

1. prospective
2. retrospective
3. none of these

3.The cumulative incidence of breast cancer among women receiving estrogen therapy is:

1. 0.2
2. 0.3
3. 0.4
4. 0.6
5. 0.8

4.The cumulative incidence of breast cancer among women who did not receive estrogen therapy is:

1. 0.05
2. 0.2
3. 0.4
4. 0.6
5. 0.8

5.The relative risk associated with estrogen therapy in this study is:

1. 0.25
2. 0.33
3. 0.5
4. 2
5. 3

Answer 1

Answer 1

Answer is Option "d" .. COHORT STUDY

As the study is undertaken before the onset of disease and the proceeds from exposure to outcome its a cohort study, as the disease has not occurred at the time of start of study.

Why the answer is Cohort study-

COHORT STUDY is a type of analytical study undertaken to refute or support the existence of association between suspected cause and disease. The study proceeds from Exposure to outcome

Also known as PROSPECTIVE STUDY/ INCIDENCE STUDY/ FORWARD LOOKING STUDY.

Distinguishing features are-

• Cohorts are identified prior to appearance of disease under investigation.
• The study groups , so defined are observed over a period of time to determine the frequency of disease in them .
• The Study proceeds forwards from Cause to effect

CASE CONTROL STUDY

Also called as Retrospective study

It is an Analytical study design

These are first approach to test casual hypothesis .

Distinguishing features are-

• Both exposure and outcome[ disease] has occured before the start of study
• The study proceeds backwards from effect to cause.
• It uses a control or comparision group to support or refute an inference.

CROSS SECTIONAL STUDY

It is the simplest form of an observational study based on single examination of a cross section of population at one point of time.

Also called Prevalence study

ECOLOGICAL STUDY

They are type of descriptive studies

Group is the unit of study with no individual level of information on the distribution of exposure and disease.

ANSWER 2

Option " a"

It is a prospective study design ad it proceeds from

Exposure to outcome.

Answer 3

Cumulative incidence of Breast cancer among females receiving estrogen therapy-

CUMULATIVE INCIDENCE

= number of new cases

Population at risk

=cases developed after taken Estrogen therapy

Population receiving therapy

= 300/500

= 0.6

Answer - 0.6

ANSWER 4

Cumulative incidence of Breast cancer among females not receiving estrogen therapy-

= Female who developed breast cancer and were not on therapy / population at risk

= 100/ 500

= 0.2

Answer - 0.2

ANSWER 5

Relative risk= Incidence of disease in exposed

Incidence of disease in non exposed

Incidence of disease in exposed = 300/500

As 300 females developed breast cancer and were on estrogen therapy and total females in study with estrogen therapy are 500

Incidence of disease in non exposed = 100/500

As 100 females did not receive estrogen therapy but they developed breast cancer. Total females who did not receive therapy is 500

Relative risk = 300/100

= 3

Answer- Relative risk is 3