Ora Paltiel, MD, MSc Braun School of Public Health & Community Medicine Hebrew University of Jerusalem Hadassah Medical Organization Israel

Epidemiological Reasoning Using Cancer Statistics Or, how to use descriptive statistics to raise hypotheses

Issues to be discussed Validity of data Reporting Confounding Effect modification Using Descriptive Data Burden of Disease Planning Hypothesis raising Measuring progress

What are the objectives of epidemiology? 1. To determine the extent of disease (states of health) and/or behaviors in the community. 2. To identify the etiology or the cause/s of a disease and the risk factors - that is, factors that increase a person’s risk for a disease. 3. To study the natural history and prognosis of disease.

4. To evaluate new preventive and therapeutic measures and new modes of health care delivery. 5. To provide the foundation for developing public policy and regulatory decisions relating to public health problems. Objectives of epidemiology

“When we measure, we know better” - Center for Disease Control (CDC), Atlanta, Georgia,USA

The epidemiological tool-box

Kaposi sarcoma in New York

The context of disease reporting

Lowest cancer death rate In the Former Yugoslav Republic of Macedonia, only 6 people per 100,000 of population die from cancer each year

Lifetime risk of developing breast cancer,

YEARONE IN… Source: American Cancer Society, 1991 Lifetime risk of developing breast cancer, cont’d

Descriptive epidemiology - hypothesis raising rarely provides enough evidence for causation Person: characteristics for study include: Age Gender Religion Marital status Ethnicity Occupation Socio-economic class Heredity vs. Environment

Age-specific rates of Breast Cancer Mortality

Russian FederationIsrael Population Pyramids 1998

Trends of Cervical Cancer Mortality in Europe and North America

Age-standardized cervical cancer death rates (and 95% confidence intervals) per women in urban Canada by neighbourhood income quintile from 1971 to Q1 = richest Q5 = poorest.

Place and time Time trends - raise hypotheses regarding environmental factors or results of medical care Geographic variation - on small + large scale, environmental  genetic factors Study of migrants: important for separating environmental from genetic factors

Numbers of cases of cancer at 16 anatomical sites in developed and in developing countries, with relative ranks

Lung Cancer Mortality for Women 1998, ASR/100000

Lung Cancer Mortality for men 1998, ASR/100000

Age-adjusted cancer death rates, males by site, US,

Age-adjusted cancer death rates, females by site, US,

Estimated annual percent changes in mortality from all types of cancer in the US over 2 periods and , according to age group

Japanese colon cancer incidence: JapanHawaiiCalifornia -  rate is affected by age at immigration - for breast cancer: 2 generations required for  rate Place and time cont’d Low Intermediate High

Biases in migrant studies 1) Different reporting 2) Different diagnostic criteria 3) Migrants are selected group

Clinical observation Descriptive data Hypothesis raising Where does evidence come from?

Clinical observation Descriptive data Hypothesis raising Analytical studies Hypothesis testing