The epidemiological tool-box A ssociations – quantification using rate ratios, rate differences,...

The epidemiological tool-box

•Associations – quantification using rate ratios, rate differences, odds ratios

The association between quantity of salt sold and oesophageal cancer mortality in counties of Henan province, China

Analytical epidemiology 1: Ecological Studies

Prevalence of carriers of hepatitis B surface antigen

Risk for cancer of the liver (cases/100000 population in areas of high risk for this cancer - sub

Saharan Africa and eastern Asia

• Biases – information bias, selection bias

• Confounding – detection and control

• Determination of causation

• Effect Modification/ Interaction/Synergism


Outcome Status

present

absent

Exposure

Status

exposed

not expose

d

2*2if only life were so simple…

Design of a case-control study

TIME

direction of inquiry

Population

Cases with disease

Controls without disease

Exposed

Exposed

Unexposed

Unexposed

Odds ratio and corresponding 95% confidence (stratified by age)

Analytical Studies 2: Case control study of Hepatitis C seropositivity and lymphoma

Design of a cohort studyDesign of a cohort study

TIME

direction of inquiry

people exposed disease

population without the no disease

disease

not exposed disease

no disease“at risk”

Analytical studies 3:Cohort of British Doctors

Death by lung cancer Current smoker Non smoker

Yes a (4,180) b (224)

No c (45,820) d (39,776)

# at beginning 50,000 40,000

Total 90,000

Relative risk: risk in exposed/risk in unexposed

RR = a b = 0.084 .0056 = 14.9 a+c b+d

Attributable risk = risk difference = excess risk in smokers

=0.084 - 0.0056. = 078

Cohort of British Doctors cont’d

Analytical studies 3: Shanghai - cohort study

18,000 men-synergy(Qian G-S et al, Can Epid Biom. Prev

1194;33)

A. Urinary Aflatoxin –

DNA adducts

B. Hepatitis B A+B

RR liver cancer

3.4 7.3 59.4

Note: Aflatoxins measured by adducts, interview unreliable

Effect Modification (or Interaction) is said to occur

when the association between exposurex and outcomey differs

by variablez

Prevalence of Actinic keratosis in Israeli Dermatologic Patients

with and without Psoriasis

Psoriatics

409 (89%)

51 (11%)

Controls

538 (73%)

200 (27%)

What is actinic keratosis?

• Rough scaly spots on sun-damaged skin

• Pre-cancerous (can give rise to Squamous cell caricnoma SCC)

• Found on nose, cheeks, upper lips, temples, forehead

• Common in fair-skinned people and those in outdoor occupations

Adjusted odds ratios (OR) for solar keratosis by hair color comparing psoriatics and

controls

7.7009

0

2

4

6

8

Black Brown Blonde/red

Psoriatics

Controls

Adjusted for ethnic origin, gender, age and degree of sun exposure

Adjusted odds ratios (OR) for solar keratosis by propensity to sunburn comparing

psoriatics and controls

7.7009

Adjusted for ethnic origin, gender, age and degree of sun exposure

0

1

2

3

4

5

Never Often/always

Psoriatics

Controls

Sometimes

•Formulating study question

•Gathering data

•Hypothesis testing

• Impact measures


• Judging the methodology

•Kappa statistic & Reliability

•Life Expectancy – survival analysis, life table analyses


•Measurement accuracy

•N = sample size

•Outcome Measures

•Proportional mortality/morbidity


•Quality of data (and/or life!)

•Randomization; Risk – incidence, types of incidence, incidence vs. prevalence, crude vs. disease-specific


•Standardization

•Time Trends

•Utility assessment

•Validity

•Weight of evidence


• X-axis

• Y-axis and plotting the data

• Z-score and statistical inference

• Ж - ?????


Steps in Designing and Conducting an Epidemiologic Investigation

You have made an observation based on

descriptive cancer statistics.……

• Specify TOPIC and PURPOSE

• Determining what is KNOWN and UNKNOWN

• State the CASE FOR ACTION

• Formulate STUDY OBJECTIVES• Formulate HYPOTHESES

“There are two possible outcomes: If the result confirms the

hypothesis, then you've made a measurement. If the result is

contrary to the hypothesis, then you've made a discovery”

- Enrico Fermi, Physicist, 1901-1954

•Select appropriate STUDY DESIGN

•Choose & define STUDY VARIABLES

•Define STUDY POPULATION & SELECTION TECHNIQUES

•Develop DATA COLLECTION TOOLS

•PRETEST developed instruments

•TRAIN FIELD WORKERS

• CONDUCT/MONITOR FIELD WORK

• Prepare data for ANALYSIS

•ANALYSE the data

•WRITE-UP findings

•COMMUNICATE findings

• INCORPORATE results into health planning

•EVALUATE modified health program

It is easier to investigate problems than to solve

them.

BUT…

It’s not so easy to study them either!

The epidemiological tool-box A ssociations – quantification using rate ratios, rate differences,...

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