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

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