2. Introduction & types of Cross sectional study
Design of Cross sectional study
Steps in Cross sectional study
Biases in Cross sectional study
Analysis of Cross sectional study
Advantages & Disadvantages of Cross
sectional study
3. An observational analytical study
Also known as prevalence study
Snapshot study
Both exposure & disease are determined
simultaneously
More useful for chronic than short lived
diseases
Tells about distribution of disease in the
population rather than its aetiology
4.
5. May be
– Descriptive
– Analytical
At descriptive level, it yields information about a
single variable or about each of number of separate
variables in a study population
At analytical level, it provides information about the
presence and strength of associations between
variables, permitting testing of hypothesis
7. Identify the reference population
Determine minimum sample required
Select study subjects through appropriate
sampling procedure
Defining Inclusion/Exclusion criteria
Diagnostic criteria for disease should be
clearly defined
Data collection
Analysis
8. Coverage evaluation survey in EPI
Cataract survey by trained paramedics
Identification of LBW infants by TBA
9. Choice of sampling frame
Non – response
Information bias
Observer bias
10. Analysis of cross sectional study is done in
terms of
1) Prevalence
2) Rate ratio (Prevalence ratio)
11. Total number of cases (old + new) existing at a
given point in time or over a period of time in
a particular population under study.
Point Prevalence
Types
Period Prevalence
12. Total no of cases at a given point in time X 100
Estimated population at the same point in time
Prevalence is a proportion expressed in terms
of percentage.
13. Total no of cases during a given period of time interval/
Estimated mid interval population at risk X
100
Less commonly used measure of prevalence
Includes the cases arising before but extending into or
through to the year as well as arising during the year.
14.
15.
16. Rate ratio = Prevalence among exposed
Prevalence among non exposed
= a/a+b
c/c+d
17. In a study to assess prevalence of hypertension
among adult male population, 1000 men
above 30 years were examined. Detailed
history of life style was asked to them. BP
recorded as per WHO guidelines and
hypertensives were identified by JNC
guidelines. The data is as follows:
18. HTN + HTN - Total
Smoking +
120
(a)
280
(b)
400
(a+b)
Smoking -
30
(c)
570
(d)
600
(c+d)
Total
150
(a+c)
850
(b+d) 1000
Prevalence of HTN among smokers = 120/400 = 0.3
Prevalence of HTN among non smokers = 30/600 =
0.05
Rate ratio = 0.30/0.05 = 6
Interpretation – HTN is 6 times more prevalent
among smokers than non smokers.
19. Provides estimate of disease burden
Relatively short duration
Easy and quick
Less costly
Useful for chronic disease with low case
fatality
Allow a risk statement although not precise
20. Does not give incidence
No direct estimate of risk posssible
Rare disease, short duration and high case
fatality not detected
Natural history of disease information is
minimal
Not possible to establish temporality
Weak design to prove causality
21. K Park Textbook of Preventive & Social
Medicine (24th Edition)
Epidemiology by Leon Gordis (5th Edition)