community health nursing

2.  It can be determined that whether statistical
association exists between the suspected
factor and disease or not and if exists, then
what is the strength of the association.

3. 1. RETROSPECTIVE STUDIES (CASE CONTROL
STUDY)
2. PROSPECTIVE STUDIES(COHORT STUDY)

4. CASE CONTROL STUDY
 This is used to test causal hypothesis

5. RETROSPECTIVE STUDIES (CASE
CONTROL STUDY)
 FEATURES
 1. Before the initiation of study the disease has
occurred due to exposure of agents
 2.The study proceeds backward.(Effect to cause)
 3. The case control study has one control group. It
involves Two population
 CASE
 CONTROL

6. 2X2 TABLE OF CASE CONTROL
STUDY
Factors responsible for
disease
Case Control
PRESENT A B
ABSENT C
A+C
D
B+D

7. STEPS OF CASE CONTROLSTUDY
 1.SELECTION OF CASES & CONTROL
 2.MATCHING
 3.MEASUREMENT OF EXPOSURE
 4. ANALYSIS & INTERPRETATIONS

8. Selection of case
 Criteria for Selecting a Case
 1. Clear definition of Case
 2. Case should meet Diagnostic & Eligibility Criteria
 3.Diagnostic criteria &stage of disease must be
specified before conducting the study.
 4. 3.Diagnostic criteria should be same throughout the
study.

9. Selection of control
 Selection of control
 1. The Person should be free from disease
 2.Control should meet the criteria expect disease such
as age, Sex, Occupation etc. the same as case


10. Matching
 Matching means a process of selection of control in
such a way that they are similar to cases with regard to
certain variables.
 Group Matching
 Pair Matching

11. Group Matching
 Within Groups, subcategories,
 Age
 Sex
 Social Class
 Occupation

12. Pair Matching
 For each case, a control is chosen which can be
matched.

13. 3.MEASUREMENT OF EXPOSURE
 Interview Schedule
 Questionnaire
 Records such as hospital records

14. ANALYSIS
 EXPOSSURE RATE
 ESTIMATION OF RISK

15. EXPOSSURE RATE
 IN CASES
 Exposure rate=a
 a+c
 ( The ratio of the no. of individuals who became case after
exposure to suspected etiological factors to the total no of
cases)
 IN CONTROLS
 Exposure rate= Controls with suspected factors
 Total No. of Controls
 Exposure rate=b
 b+d

16. Smoking and Lung Cancer
Cases Control Total
Smokers 33(a) 55(b) 88(a+b)
Non Smokers 2(c) 27(d) 29 (c+d)
Total 35 (a+c) 82(b+d)

17. Exposure rate
 Cases = a/(a+c)= 33/35=94.2 Per cent
 Control= b/(b+d)= 55/82 =67.0 Per cent
 Frequency of lung cancer was definitely higher among
non smokers


18. ESTIMATION OF RISK
 Relative risk
 Incidence among exposed
 Incidence among non exposed
 ODD Ratio
 Cases with suspected factor
 = Total no. of cases

19. Odd ratio Cross product Ratio
ad/bc
Disease No
exposed a b
Not exposed c d

20. Odd ratio
 (a/b)/(c/d) = ad/ bc
 33 x27/55x2=8.1

21. COHORT STUDIES
 It is an analytical study which provide additional
evidence to accept or reject the existing association
between suspected cause and disease.

22. Concept of Cohort
 Cohort is a group of people who share common
characteristics. It can be a group of people who
experience common characteristics with in a defined
time period.

23. Types of cohort
 Exposure cohort
 It is a group of persons exposed to a common drug or
infection with in a defined period
 Marriage Cohort
 It is a group of males or females married on the same
day.

24. Occurrence of disease in relation to
 TIME
 1.Prospective Cohort Studies
 2.Retrospective Cohort Studies
 3. A combination of both

25. 1.Prospective Cohort Studies
 Starts from present and continue in to future
 Disease of the individual has not yet occurred at the
time of investigation starts. The disease result in the
future.

26. 2.Retrospective Cohort Studies
 In which the outcome( disease) has occurred before
the start of investigations. It is the study of going back
in time.

27. Combination of both retrospective
and prospective studies
 In this group is identified from past records and is
assessed up to present and is followed up into future
for assessment of outcome.

28. Steps of Cohort Study
 1.Select study subjects
 2.Collect data
 3.Select Comparison group
 4. Follow up
 5.Analysis

29. 1.Select study subjects
 Subject for cohort study can be selected either from
general population or special groups of population.
 A.General population
 Large samples

30. B. Special groups of population.
 1. Select Groups –professional groups and are
homogenous in nature. –doctors, nurses, teachers
 2. Exposure Groups
 Cohort is selected because of special exposure to
physical, chemical another disease agents.

31. Collect Data
 1.Personal interview
 2.Mailed questionnaire
 3.Review of records
 4.Medical tests
 5.Environmental surveys.

32. Select a comparison Group
 In order to compare morbidity and mortality rates.
 The comparison Group can be in built or the external
group or the general population.
 Internal Comparison – based on the degree of
exposure of risk factors
 .

33. Internal comparison
Degree of exposure No of deaths
½ pack 24
½ - 1 Pack 84
1-2 pack 90
2 pack 97

34. B. External Comparison-
 outside comparison group is required. When
information on degree of exposure is not available, it is
necessary to put up an external control, to evaluate the
experience of the exposed groups.
 E.g., smokers and non smokers,
 C. Compari son with general Population in the same
geographic area.

35. Follow Up
 Periodic check up and investigations
 Reviewing records
 Routine surveillance mortality records

36. Analysis
 Find out the risk rate and frequency of the new cases
in terms of incidence rate
 Incidence rate = No of new cases of specific disease
 during a given period x 1000
 Population at risk during that period

37. Incidence rates
a) smokers 70/7000= 10 per 1000
b) Non Smokers 3/3000=1 per 1000
Cigarette
smoking
Developed lung
Cancer
Did not develop
lung Cancer
Total
Yes 70(a) 6930 7000
No 3(c) 2997 (d) 3000

38. Estimation of risk
 Relative risk
 Attributable risk

39. Relative risk
 Incidence among exposed
 Incidence among non exposed
 RR of Lung cancer 10/1=10
 so It is a direct measure of the strength of the
association between suspected cause effect.
 Relative risk of one indicates no association. Relative
risk greater suggests positive association.

40. Attributable Risk
 It is calculated by subtracting the incidence of disease
rate among non exposed from incidence of exposed
and by dividing this by incidence rate of exposed and
multiplied by 100. in order to get the result in
percentage.

41. Attributable risk
 Incidence of disease rate among exposed- incidence of
disease rate among non exposed x100
 Incidence rate among exposed
 10-1 x 100 90 per cent
 10