Type of epidemiological Study designs

1. PRD-1
Cross-sectional
Studies
Introduced by
Dr. Nermin Osman
Assistant Lecturer of Medical Statistics,
MRI, Alexandria University
United Nations System Staff College
Intern-UNITAR

2. PRD-2
Definition
• Measurement of exposure of interest and
outcome of interest is carried out at the
same time (e.g. Obesity and Diabetes)

3. PRD-3
Which came first?
?? Causality
There is no in-built directionality as both exposure and
outcome are present in the study subject for quite some
time

4. PRD-4

5. PRD-5
֍What is your research hypothesis?

6. PRD-6

7. PRD-7
Cross-sectional studies
• May be
– Descriptive
– Analytical or
– Both
• At descriptive level, it yields information about a
single variable, or about each of number of
separate variables in a study population
• At analytic level, it provides information about
the presence and strength of associations
between variables or comparison between
cases and control according to certain risk
factor, permitting testing of hypothesis

8. PRD-8
Synonyms
Prevalence study

9. PRD-9
Prevalence
• Prevalence proportion: Proportion of the
subjects who have the disease at a point in time
• Example:
– Of 1500 middle aged women 30 had diabetes on
January 1, 2007.
– The prevalence proportion of diabetes was 30/1500 =
0.02 or 2%

10. Prevalence:
The function of the incidence and the duration of the disease
PRD-10

11. PRD-11

12. PRD-12

13. PRD-13
Prevalence & incidence
Number of all (old +new cases) in certain area at a given time
P = -------------------------------------------------------------------------------------
Number of population at risk in the same area and time
Number of new cases in certain area at a given time
Incidence= --------------------------------------------------------------------------------
Number of population at risk in the same area and time
x 100

14. PRD-14
Cross-Sectional Studies
Advantages
• Cheap and quick studies.
• Data is frequently available through
current records or statistics.
• Ideal for generating new hypothesis.

15. PRD-15
Cross-Sectional Studies
Disadvantages
• Temporal weakness:
– Cannot determine if cause preceded the
effect or the effect was responsible for the
cause.