Introduction to Epidemiology

January 21, 2015

Fresno State University

Paul K. Mills, Ph.D., M.P.H.

Epidemiology

• The study of the distribution and determinants of disease in human populations.

• Distribution-how disease is distributed in the population by characteristics of person, place and time.

• Determinants-what “risk factors” increase or decrease risk of specific diseases.

Types of Epidemiology

Measures of incidence and prevalence

Discriptive

The Distribution of Disease

Measures of exposure-disease association (RR & OR)

Analytic Epi

The Causes of Disease

Epidemiology

The study of distribution and determinants

Descriptive and Analytic Epidemiologic Studies of Cancer

• Descriptive Studies• Cancer Incidence and Mortality

Rates in the Hmong population of California.

• Cancer Incidence rates and cancer Survival in the South Asian

population of the U.S.

• Analytic Studies• Population based case-control

studies of epithelial ovarian cancer in the San Joaquin Valley.

• Nested case-control studies of agricultural exposures and cancer in a cohort of farm workers (UFW

Study).

Descriptive Epidemiology

• How is disease distributed in the community by aspects of:

• Person (age, race/ethnicity, gender).

• Place (geography, macro and micro scale).

• Time (secular, temporal changes on daily, seasonal, yearly or longer time periods)

Analytic Epidemiology

• What are the “risk factors” that alternatively increase or decrease risk of disease in humans?

Number of new Cases of Cancer and Cancer Deaths in Fresno county, the state of California, the U.S, and Worldwide, 2010

New Cases Deaths

Fresno county 3035 1210

California 134,000 54,655

United States 1,479,000 562,340

Worldwide 10,800,000 7,600,000

Population Growth in the San Joaquin Valley, 1988-2006

0

500000

1000000

1500000

2000000

2500000

3000000

3500000

'198

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9

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0

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5

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0

'200

1

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2

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3

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4

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5

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Year

Po

pu

alt

ion

Population Growth in the San Joaquin Valley, 1988-2006 by Race/Ethnicity

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1,400,000

1,600,000

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

Year

Po

pu

lati

on NH White

NH Black

Hispanic

NH Asian/PI

0

5000

10000

15000

20000

25000

Number/yr.

Number of New Cases & Deaths, Top Ten Cancers in California, 2009

New cases

Deaths

Worldwide Distribution of Most Frequent Cancers

The Importance of Age Adjustment

Copyright ©2005 American Cancer Society

From Parkin, D. M. et al.

CA Cancer J Clin 2005;55:74-108.

FIGURE 5 Age-standardized Incidence Rates for Lung Cancer

Age-adjusted Incidence Rates of Lung and Bronchus Cancer in California, 1988-2007

Age-adjusted Incidence Rates for Lung and Bronchus Cancer in California, 2003-2007, by Race Ethnicity

0

10

20

30

40

50

60

70

80

90

NH White NH Black Hispanic NH Asian/PI

Deaths/100,000

Age-adjusted Mortality rates from Lung Cancer in California, 2003-2007, by Gender and Race/Ethnicity

Male Rate

Female Rate

0

2

4

6

8

10

12

14

16

18

20

Males Females

Percent

Gender

Current Smoking Prevalence (%), SJV and California, 2007, by Gender (CHIS,2007)

SJV

California

Analytic Epidemiology

• What are the “risk factors” that alternatively increase or decrease risk of disease in humans?

Causes of Cancer Deaths in the U.S. (Adapted from the Harvard Report on Cancer Prevention, 1996).

0

5

10

15

20

25

30

Percent

Tobacco

Diet/Obesity

Inactivity

Occuaption

Family Hx Ca

Viruses/Bacteria

Perinatal

Reproductive

Alcohol

SES

Env.Pollution

Ionizing/Solar rad.

Pres. Drugs

Salt/Food Additives

1775: Percival Pott linked scrotal cancer to chimney sweeps exposed to soot

Female Farm Worker in California

Mortality Ratios in Farm Workers for Transportation Injuries and Other Injuries

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

MVT driver

(142)

MVT

passenger (67)

MVT

pedestrian (77)

MVT other (67) Other Injury-

Machine (15)

PM

R

Fresno Bee, June 28, 2010

Liver Cancer Incidence in California, 2003-2007

Screening for Disease

Screening for Disease

• Criteria for a screening test.

• Measures of Sensitivity and Specificity

• False positive and False negative.

• Effect of disease prevalence on Predictive value.

Measures of Disease, Exposure-Disease Association and Disease Impact

• Incidence and Prevalence

• Relative risk

• Odds Ratio

• Standardized Mortality Ratio (O/E)

• Attributable risk

Ambient Air Quality in the San Joaquin Valley

Study Design Issues in Epidemiology

• Prospective cohort study (e.g. Framingham Heart Study, Nurses Health Study)

• Retrospective case/control study (aka case/referent study).

• Cross-sectional or prevalence study.

• Ecologic study.

• Case series

Assessing Confounding in any E-D relationship

• Definition of confounding

• Detection of Confounding

• Adjustment for confounding (Stratification and/or modeling)

Evaluation of Disease “clusters” in the Community

• Question: how much and what type of disease is present?

• Is the amount of disease more than would be “expected”

• Is the type of disease unusual?

Data Quality Issues in Epidemiology

• Beyond Confounding and Effect Modification.

• Data Validity (internal& external)

• Data Precision (width of the CI)

• Reliability (reproducibility)

Assessing Causality

• Biologic plausibility

• Magnitude and direction of alterations in risk

• Dose-response relationship

• Effect of cessation or removal of suspected cause

• Temporality