Post on 19-Jun-2020
Epidemiological Study Design: OverviewEpidemiological Study Design: Overview
Lakkana Thaikruea, MD., Cert of FETP, M.S., PhD. Community Medicine Department, Faculty of Medicine, CMU
Readings
Thaikruea L. Chapter 3 Types of Epidemiologic Studies. In: Basics of Epidemiology. Ungchusak K, editor, Bangkok: Canna Graphic Publishing; 2014 p 52-79. ISBN 978-616-91574-1-0Thaikruea L. Chapter 5 Confounding and Bias. In: Basics of Epidemiology. Ungchusak K, editor, Bangkok: Canna Graphic Publishing; 2014 p 118-129. ISBN 978-616-91574-1-0Thaikruea L. Handout of Apply epidemiology for various fields5.10fields5.10Gordis L Epidemiology. 5th Ed, Philadelphia: ELSEVIER Saunders, US. 2014Szklo M and Nieto FJ. Epidemiology: beyond the Basics. Jones & Bartlett Publishers. 2014.Principles of Epidemiology in Public Health Practice: An Introduction to Applied Epidemiology and Biostatistics. Third Edition. CDC, Atlanta: 2008.Bonita R, Beaglehole R, Kjellström T. Basic epidemiology. 2nd ed. Geneva: World Health Organization; 2006. http://oknation.nationtv.tv/blog/lakthai
Usefulness of descriptive epidemiology
• Understand the distributions of the
disease and get insights on its pattern
• Predict trend of the disease
• Generate hypothesis for analytic
epidemiology
Epidemiology
The study of distribution and determinants of health-related states or events in specified populations, and the application of this study to control of the health problemshealth problems
Study: includes surveillance, observation, hypothesis testing, analytic research, and experiments.
Last JM. A Dictionary of Epidemiology. 1995.
Epidemiology (Con.’t)
Distribution:
analysis by time, place, and classes of persons affected
Determinants:
all the physical, biological, social, cultural, all the physical, biological, social, cultural, and behavioral factors that influence health
Health-related events:
include disease, causes of death, behavior, reaction to preventive regimens, and provision and use of health services
Type of Type of Epidemiological StudiesEpidemiological Studies
What are common types of
How can be distinguish type (or design) of an
epidemiological study?
What are common types of epidemiological studies?
Answer two questionsAnswer two questions
1) Can researcher allocate primary exposure ?
No
Yes
If ‘Yes’
2) Does researcher allocating participants using randomization?
No
Yes
Randomization
To prevent potential bias on the part of researcher (assigns participants into different exposure groups)
Increase comparability (BUT not guarantee) Increase comparability (BUT not guarantee)
– measurable variables
– non-measurable variables
AssignExposure
Conduct Randomization
Yes No
Yes Experiment Quasi Experiment
No -------- Observational Study
Observational studyObservational study
Researcher measures what happened but
does not intervene
Observational study designs
population, outcome measureLongitudinal Cross-sectional
Samplingscheme
Complete Cohort cross-scheme
Complete Cohort cross-sectional
Incomplete case-control
(incident cases)
case-control(prevalent
cases)
Type of observational studiesType of observational studies
1. Descriptive
• Lack/ little of knowledge about a health problem/ determinant
• Aim to describe occurrence of a health problem/ determinantdeterminant
2. Analytic
• Enough knowledge about a health problem/ determinant
• Aim to test specific etiologic hypothesis, justify more studies, or recommend intervention
Descriptive study
• Often be the first step in an epidemiological investigation
• Describes the occurrence of a health problem / determinant in a population by time, place, and person
• Describe pattern and trend of a health • Describe pattern and trend of a health problem / determinant
•Study designs:
• Case series
• Ecology
• Cross-sectional
Answer to the questions
To WHOM does it happen?
WHERE does it happen? WHERE does it happen?
WHEN does it happen?
HOW does it happen?
Cases
0
5
10
15
20
25
0
200
400
600
800
1000
1200
0-4 '5-14 '15-44 '45-64 '64+
Person Place Time
0
1 2 3 4 5 6 7 8 9 100-4 '5-14 '15-44 '45-64 '64+
Age Group
Evaluate information
Pathogen? Source? Transmission?
Generate hypothesis
1. PERSON
Factors associate with pattern of disease occurrence, severity, interaction, etc.
AgeGender
1. PERSON
Gender Race Socioeconomics Occupation
Marital status Size of a family Behavior
PERSON (con.’t)
Behavior Others; blood group
2. PLACE
2.1 Geographic
Environment
Separate race
2. PLACE
Example of Arbovirus:
- America; California Encephalitis
- Africa; Ebola
-South East Asia; Dengue
2.2 Government/policy
Development
Sanitation
2. PLACE (Con.’t)
Example of vector-borne disease:
- rural
- urban
3. TIME
3.1 Secular Trend- “Changes over a long period of time,
generally years or decades”*
- Caution: may be due to medical interest,
3. TIME
- Caution: may be due to medical interest, diagnostic methods, report methods, or census
* Last JM. A Dictionary of Epidemiology. 1995.
3.2 Cyclicle
- Seasonal: “Annual cycling of incidence ona seasonal basis.”*
- Secular: “Fluctuation in disease incidence
3. TIME (Con.’t)
- Secular: “Fluctuation in disease incidence over a period longer than a year”
* Last JM. A Dictionary of Epidemiology. 1995.
3.3 Cluster
- “Aggregation of relatively uncommonevents or diseases in space and/or timein amounts that are believed orperceived to be a greater than could be
3. TIME (Con.’t)
perceived to be a greater than could beexpected by chance..”*
- Example: Sudden Cardiac Death in Yunnan Province
* National Conference on Clustering of Health Events. Am J Epidemiol 1990
Example: Sudden Cardiac Death in Yunnan Province
Trend and Pattern of Disease
The trend of disease is the description of disease occurrence over several time points, e.g., stable, increasing or decreasing decreasing
The patterns of disease can be observed over time and we describe them in terms of person, place and time
29
Rabies in animal (Jan – 20 Aug 10)
765 sample were tested; 182 confirmed (23.8%)
70.00%
80.00%
90.00%
100.00%
140
160
180
200
0.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
0
20
40
60
80
100
120
140
Jan Feb Mar Apr May Jun Jul Aug
Tested Positive positive percentage
Source: P. Srisai, 2010
30
NS 1NS 2
Epidemic curve and spot map of mumps
cases, kindergarten “A”, May–September 1999 (N=38)
1 / 1 1 / 2 3 / 2 3 / 1
Weekly interval
2 / 2 Kit.
1 child case 1 officer case
2 / 1
Laosirithaworn, 199931
Analytic Study
Analytic study
• Enough knowledge about a health problem/ determinant
•Aim to:
• Test specific etiologic hypothesis • Test specific etiologic hypothesis
• Justify more studies
• Recommend intervention
• Study designs:
• Basic:
• Case-control
• Cohort: Prospective, retrospective, and historical cohort
• Advance:
• Experiment
• Quasi-experiment
• Matched case-control
• Hybrid: combination of
• cross-sectional and cohort
• case-control and cohort
Basic Study Design Summary
Study design
ObservationalExperimental
Descriptive Analytic
Quasi-experimental
Case/ serial cases
Cross-sectional
Ecological
Serial cross-sectional
Ecological
Cohort
Case-control
Elderly woman
11stst year Medical studentyear Medical student
Time and tidewait for no manwait for no man
ขอให้สวัสดีSawasdee