Clinical EpidemiologyCommunity Health and Environmental Medicine 3

Joko MulyantoDepartment of Public Health & Community MedicineJenderal Soedirman University School of Medicine

Introduction

• Epidemiology is basic science concerned with the pattern of disease in human population.

• Distribution of disease by person, place, and time.

• Assumptions - Disease does not occur randomly- Disease has identifiable cause

> can be altered> prevent from development

Epidemiology is defined as…

The study of the distribution and determinants of health-related states or events in specified population, and the application of this study to control of health problems.

Epidemiology is defined as… (cont’d)• Study

surveillance, observation, hypothesis testing, analytic research, and experiments.

• Distribution analysis by time, place, and person.

• Determinants physical, biological, social, cultural, and behavioral factors that influence health.

• Health-related states or events diseases, causes of death, behavior, reactions to preventive regimens, and provision and use of health services.

Epidemiology is defined as… (cont’d)• Specified populations

those groups of people with identifiable characteristics

• Application to controlrefers to the goal of epidemiology, that is to assess the public health importance of diseases, identify the population at risk, identify the causes of disease, describe the natural history of disease, and evaluate the prevention and control of disease

Clinical Epidemiology

• Applying population-based information to optimize patient care.

• Use epidemiological methods in clinical setting.

• The basis of evidence-based medicine.

How is epidemiology used in clinical medicine ?• Describe the natural history of disease.• Discuss the causality of disease.• Provide disease surveillance.• Evaluate diagnostic testing.• Evaluate therapy of disease• Evaluate prognosis of disease.• Economic evaluation and decision

analysis.

Observational & Analytical Epidemiology• Descriptive epidemiology

- The occurrence of disease• Etiological epidemiology

- Cause of disease• Experimental epidemiology

- Assessment of therapy

Epidemiological analysis

• Measure of disease frequency.• Magnitude of association.• Statistical association.• Regard to bias, confounding, and

chance.

Research Designs Used in Epidemiology• Case reports / case series• Case control• Cross-sectional• Cohort : Prospective and

Retrospective.• Randomized Clinical Trial (RCT)• Secondary analysis

Epidemiologic Terms

• Chance• Bias• Confounding• Frequency measure• Measure of association.• Causal inference.

Chance

• “Luck of the draw”• Concept of inference• Hypothesis testing (p – value)• Confidence interval

Bias

• Systematic errors in collecting or interpreting data such that there is deviation of results or inferences from the truth.

• Bias results from systematic flaws in study design, data collection, or the analysis or interpretation of results.

Type of Bias

• Selection Bias.Non-comparable criteria used to enroll participants.

• Information Bias.Non-comparable information is obtained from the study groups due to interviewer bias or due to recall bias.

Confounding• a mixing of effects between the exposure and

the disease - by other factors associated with both the exposure and the disease- the effects of the two processes are not separated

• Confounding results when the effect of an exposure on the disease (or outcome) is distorted because of the association of exposure with other factor(s) that influence the outcome under study.

Confounding (cont’d)

Gambling Cancer

Smoking,

Alcohol

observed association, presumed causation

unobserved association true association

Frequency Measurement

• General measurement of frequency- Ratio- Proportion- Rate

• Frequency measurement in epidemiology- Prevalence

- Incidence

Prevalence

• the number of existing cases in the population; the proportion of the population at a given time that have the factor of interest.

Type of Prevalence

• Point Prevalence; specific point of time

• Period prevalence; specific period of time

Incidence

• the probability (risk) of an individual developing the disease (outcome) during a specific period of time.

Type of Incidence

• Cumulative incidencea measure of the occurrence of new cases in a population

• Incidence densitythe rapidity with which new cases develop; one person year of experience (PYOE)

Measure of Association

• frequency measurements are compared and summarized

• to determine the magnitude of the observed association between risk factor and outcome

• useful in judging the likelihood that the exposure is a significant clinically factor in the development of the outcome of interest.

Type of Measures of Association• Ratio

- Relative Risk> Risk Ratio> Rate Ratio

- Odd Ratio • Difference

- Attributable Risk> Attributable Risk Fraction> Population Attributable Risk Fraction

Relative Risk

• Ratio of occurrence of disease in exposed to non-exposed populations.

• Risk Ratio: comparison of prevalence or cumulative incidence.

• Rate Ratio: comparison of incidence density.

Odd Ratio

• Ratio of odds of being exposed if having disease, to those of being exposed if disease free.

Attributable Risk

• Difference in risk between exposed and non-exposed population.

• Attributable risk fractionattributable risk as proportion of total risk in

exposed group.• Population attributable risk fraction.

the proportion of the population risk that is attributable to the exposure.

Causal Inference

• Natural history of disease; agent, host, environment, vector.

• Koch’s postulate of infectious disease.

• Bradford Hills postulates for multi-causal diseases

Choice of Study Design

• Disease surveillance > cross-sectional

• Natural history of disease, causality of disease> cohort study, case-control

• Diagnostic testing> SR, RCT, cohort study, case-control

Choice of Study Design

• Therapy evaluation> SR,RCT, cohort study, case control, case-series

• Prognostic evaluation> cohort study, survival analysis, case-series

Cross Sectional Study

Exposed Disease

No Exposed No Disease

CURRENT

Case - Control

Disease

No Disease

Exposed

No exposed

Exposed

No Exposed

CURRENTPAST

Cohort Study (Prospective)CURRENT Follow-Up FUTURE

Subject

Exposed

No Exposed

No disease

Disease

Disease

No disease

Cohort Study (Retrospective)

Subject

Exposed

No Exposed

No disease

Disease

Disease

No disease

CURRENTPAST

Clinical Trial

Subject

Treatment

Control

Effect ( - )

Effect (+)

Effect (+)

Effect ( - )

R

Diagnostic TestDisease

Diagnostic

Result

Yes No

Positive

Negative

TP FP

FN TN

Survival Analysis

Disease

Death

CensoredDeath

Survive

CURRENT FUTUREFollow Up

Time Interval

Survive Censored

References

MacMahon, B., Pugh, T.F. (1970). Epidemiology: Principles and Methods. Little Brown & Co.: Boston

Risser, W., Risser, J. (1999). Introduction to clinical epidemiology.

Rothman, K.J. (1986). Modern Epidemiology. Little Brown & Co: Boston.

Sastroasmoro, S., Ismael, S. ( 2002). Dasar-dasar Metodologi Penelitian Klinis. Sagung Seto: Jakarta.

Silman, A.J.Epidemiological studies: A practical guide. Cambridge University Press: London.

T H A N K Y O U

djokomoeljanto©2006