Descriptive Studies in Epidemiology: Understanding Disease Occurrence and Distribution, Study notes of Epidemiology

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EPIDEMIOLOGICAL STUDY DESIGNS

By Tilaye Workineh (MPH/Epid, Asst. Prof. of Epidemiology) Lecture 4

Objective of the course

Aug 2021 2 Descriptive Designs

 Introduction to study design



Describe the basic concepts of descriptive studies



Describe the concept of time, place and person in

descriptive studies



Describe when and how to carry out common

descriptive studies



Describe the limitations and strength of

Descriptive studies

Introduction



Research design is the overall plan which connect

the conceptual research problems to the

pertinent research outcome



Study design is action plan which portray the

strategies and tool to answer the research

question



It articulates what data is required, what methods

are going to be used to collect & data analysis, &

how all of this is going to answer your research

question.

Introduction …

 (^) Epidemiology is broadly categorized into descriptive and analytical => Corresponding action plan /design/ exist  (^) Broad categories of epidemiological studies: according to their focus of investigation

1. Descriptive studies: focus on the distribution of disease /P T P/ 2. Analytic studies: focus in elucidating the determinants of disease/cause effect relationships/

Introduction …

Descriptive Epidemiology



Description of disease occurrence, by person,

place and time



Not intended to confirm causality

Purpose: To characterize the amount and

distribution of disease within a popn

 In other words …. to identify health problems &

patterns of disease occurrence

Descriptive study designs … 

Descriptive studies generally precede analytic

studies designs which investigate

determinants of disease



Thus, descriptive studies often help to

generate research hypotheses



Describe the person, time and place of health

event occurrence

Person



Since disease does not occur at random:



What kinds of people tend to develop a

particular disease, and who tends to be

spared?



What’s unusual about those people?

Person…

Sex – biological and non-biological factors related

to sex have disease risk.

 In all developed countries, life expectancy is

higher in females than males – principally due to

lower heart disease mortality



However, many chronic diseases occur more

frequently in women (depression, lupus, etc.)

 As lifestyles continue to become more similar, a

question is whether mortality rates will become

more similar? (i.e. env’t vs biology)

Person…

Race/ethnicity – difficult to define, and to identify which characteristics may relate to disease occurrence

• Remarkable variation exists in rates of disease occurrence across racial and ethnic groups  (^) Genetics?  (^) Socioeconomic status(SES)?  Environmental exposures?  (^) Access to health care?  (^) Lifestyle factors?

Place

Investigation by place includes:



Across countries (international)



Within country variation



Urban/rural differences



Localized areas

Place…

Infectious and chronic diseases show great

variation from one country to another



Some differences may be attributed to:

 Climate

 Cultural factors

 Diet



Genetics

Time

 (^) Since disease does not occur at random:  (^) How does disease frequency change over time, and what other factors are temporally associated with those changes?  The occurrence of health-relate events can vary by time:  (^) Secular trends  (^) Cyclic fluctuations  (^) Point epidemics

Time…

Secular trends refer to gradual changes in disease

occurrence over long periods of calendar time

Example: Death from communicable d/ses has

been declining where as deaths from chronic

d/ses has been raising in some developing

countries

Cyclic fluctuations/ periodic



refer to shorter-term increases and decreases in

disease occurrence over a period of years, or

within a year.