the epidemiological tool-box a ssociations – quantification using rate ratios, rate differences,...
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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
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
The epidemiological tool-box
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
The epidemiological tool-box
• Judging the methodology
•Kappa statistic & Reliability
•Life Expectancy – survival analysis, life table analyses
The epidemiological tool-box
•Measurement accuracy
•N = sample size
•Outcome Measures
•Proportional mortality/morbidity
The epidemiological tool-box
•Quality of data (and/or life!)
•Randomization; Risk – incidence, types of incidence, incidence vs. prevalence, crude vs. disease-specific
The epidemiological tool-box
•Standardization
•Time Trends
•Utility assessment
•Validity
•Weight of evidence
The epidemiological tool-box
• X-axis
• Y-axis and plotting the data
• Z-score and statistical inference
• Ж - ?????
The epidemiological tool-box
Steps in Designing and Conducting an Epidemiologic Investigation
You have made an observation based on
descriptive cancer statistics.……
• 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