Principles of Epidemiology

Dona Schneider, PhD, MPH, FACE

E J Bloustein School of Planning and Public Policy

Rutgers University, NJ, USA

2

About the Author

Dona Schneider

3

Known Risk Factors for Cancer

Smoking

Dietary factors

Obesity

Exercise

Occupation

Genetic susceptibility

Infectious agents

Reproductive factors

Socioeconomic status

Environmental pollution

Ultraviolet light

Radiation

Prescription Drugs

Electromagnetic fields

4

Preliminary Topics Data sources and limitations for cancer

epidemiology

How much cancer is occurring?

How does occurrence vary within the population?

How do cancer rates in your area compare to that

in other areas?

Data sources and limitations for

cancer epidemiology

Review U.S. Census, U.S. Vital Statistics, SEER and NJCR data

6

Some other raceOther

Other Pacific Islander

Other Asian

Samoan

Guamanian or Chamorro

Vietnamese

Native HawaiianHawaiian

KoreanKorean

Asian Indian

FilipinoFilipino

JapaneseJapaneseJapaneseJapanese

American Indian or Alaska NativeIndian (Amer.)IndianIndian

ChineseChineseChineseChinese

QuadroonQuadroon1

Black, African American, or NegroNegro or BlackBlack of Negro decentBlackBlack

WhiteWhiteWhiteWhiteWhite

200021970190018701860

Race Categories in the Census 1860-2000

7

Revised racial and ethnic standards (effective as

of the 2000 decennial census) have 5 minimum

categories for data on race and 2 for ethnicity

Other Federal programs should adopt standards

no later than January 1, 2003

Revision of Statistical Policy Directive No. 15, Race and Ethnic Standards for Federal Statistics and Administrative Reporting

Office of Management and Budget (OMB)

8

American Indian or Alaska Native

A person having origins in any of the original people of North and South America (including Central America) and who maintain tribal affiliation or community attachment

Asian

A person having origins in any of the original people of the Far East, Southeast Asia of the Indian subcontinent including for example, Cambodia, China, India, Japan, Korea, Malaysia, Pakistan, the Philippine Islands, Thailand and Vietnam

OMB Race Categories

9

Black or African American

A person having origins in any of the black racial groups of Africa. Terms such as “Haitian” or “Negro” can be used in addition to “Black or African American”

Native Hawaiian or Other Pacific Islander

A person having origins in any of the original peoples of Hawaii, Guam, Samoa or other Pacific Islands

White

Persons having origins in any of the original peoples of Europe, the Middle East or North Africa

OMB Race Categories (continued)

10

Census Data Changes to the Race Question in the 2000 Census:

The Asian and Pacific Islander (API) category was split:a) Asiansb) Native Hawaiian and Other Pacific Islanders (NHOPI)

The category American Indian, Eskimo, Aleut (AIEA) was changed to American Indian or Alaskan Native (AIAN)

Respondents could select more than one race.

11

U.S. Census Bureau

http://www.census.gov/

12

Vital Statistics

Maintained by the National Center for Health Statistics (http://www.cdc.gov/nchs/nvss.htm)

States report the following to NCHS: Birth data (Natality) Death data (Mortality) Marriage data (no longer collected) Divorce data (no longer collected)

13

CDC Wonder

http://wonder.cdc.gov/

14

Registries for Morbidity Data

New Jersey Cancer Registryhttp://www.state.nj.us/health/cancer/statistics.htm

SEER: Surveillance, Epidemiology, and End Resultshttp://seer.cancer.gov/

15

Data Limitations

Little data is available at the local level

Problem of small numbers

Data may not be collected uniformly (race category differences, etc.)

People are mobile

Cancer has a long lag time

How much cancer is occurring?

Understand incidence rates and prevalence

17

Measuring Epidemiological Outcomes

A proportion with the specification of time

(e.g. deaths in 2000 / population in 2000)Rate

A ratio where the numerator is included in the denominator (e.g. males / total births)

Proportion

Relationship between any two numbers

(e.g. males / females)Ratio

18

Definitions

Incidence is the rate of new cases of a

disease or condition in a population at risk

during a time period

Prevalence is the proportion of the

population affected

19

Incidence

Incidence is a rate

Calculated for a given time period (time interval)

Reflects risk of disease or condition

Incidence =

Number of new cases during a time period

Population at risk during that time period

20

Prevalence

Prevalence is a proportion

Point Prevalence: at a particular instant in time

Period Prevalence: during a particular interval of time (existing

cases + new cases)

Prevalence =

Number of existing cases

Total number in the population at risk

21

Prevalence = Incidence Duration

Prevalence depends on the rate of occurrence (incidence)

AND the duration or persistence of the disease

At any point in time:

More new cases (increased risk) yields more existing cases

Slow recovery or slow progression increases the number of affected individuals

22

Incidence/Prevalence Example

For male residents of Connecticut:

The incidence rate for all cancers in 1982

431.9 per 100,000 per year

The prevalence of all cancers on January 1, 1982

1,789 per 100,000 (or 1.8%)

23

Proportional cancer incidence by gender, US 2000

How does occurrence vary

within the population?

Understand measures of association and difference

25

Outcome Measures Compare the incidence of disease among people who

have some characteristic with those who do not

The ratio of the incidence rate in one group to that in

another is called a rate ratio or relative risk (RR)

The difference in incidence rates between the groups

is called a risk difference or attributable risk (AR)

26

Calculating Outcome Measures

Outcome

D

B

No Disease

(controls)

IN = C / (C+D)CNot Exposed

IE = A / (A+B)AExposed

IncidenceDisease

(cases)Exposure

Relative Risk = IE / IN

Attributable Risk = IE - IN

27

1,1001,000100

730

370

Total

Lung Cancer

700

300

No

30/730 = 41 per 100030Non-smoker

70/370 = 189 per 100070Smoker

IncidenceYesExposure

Relative Risk = IE / IN = 189 / 41 = 4.61

Attributable Risk = IE - IN = 189 - 41 = 148 per 1000

28

Smokers are 4.61 times more likely than nonsmokers to develop lung cancer

148 per 1000 smokers developed lung cancer because they smoked

Relative Risk = IE / IN = 189 / 41 = 4.61

Attributable Risk = IE - IN = 189 - 41 = 148 per 1000

29

RR < 1 RR = 1 RR > 1

Risk comparison between exposed and unexposed

Risk for disease is lower in the

exposed than in the unexposed

Risk of disease are equal for exposed and unexposed

Risk for disease is higher in the exposed than in the unexposed

Exposure as a risk factor for the disease?

Exposure reduces disease

risk

(Protectivefactor)

Particular exposure is not a

risk factor

Exposure increases

disease risk(Risk factor)

30

Annual Death Rates for Lung Cancer and Coronary Heart Disease

by Smoking Status, Males

1000 – 500 = 500 per 100,000

127.2 – 12.8 = 114.4 per 100,000

AR

1000 / 500 = 2127.2 / 12.8 = 9.9RR

50012.8Non-smoker

1,000127.2Smoker

Coronary Heart DiseaseLung CancerExposure

Annual Death Rate / 100,000

31

Summary

The risk associated with smoking is lower for

CHD (RR=2) than for lung cancer (RR=9.9)

Attributable risk for CHD (AR=500) is much higher

than for lung cancer (AR=114.4)

In conclusion: CHD is much more common

(higher incidence) in the population, thus the

actual number of lives saved (or death averted)

would be greater for CHD than for lung cancer