.

1. Dr Abhishek Kumar
JR(A) – III
Dept. of PSM, RIMS

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

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

6. Reference
Population
Sample
Sampling
Exposure &
Outcome
Exposure & No
outcome
No exposure &
Outcome
No exposure &
No outcome
Measure
ment

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.

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)

22. Thank you