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

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Presentation on theme: "The epidemiological tool-box A ssociations – quantification using rate ratios, rate differences, odds ratios."— Presentation transcript:

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

2 The association between quantity of salt sold and oesophageal cancer mortality in counties of Henan province, China Analytical epidemiology 1: Ecological Studies

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4 Prevalence of carriers of hepatitis B surface antigen

5 Risk for cancer of the liver (cases/ population in areas of high risk for this cancer - sub Saharan Africa and eastern Asia

6 Biases – information bias, selection bias Confounding – detection and control Determination of causation Effect Modification/ Interaction/Synergism The epidemiological tool-box

7 Outcome Status absentpresent exposed Exposure Status not exposed 2*2 if only life were so simple…

8 Design of a case-control study TIME direction of inquiry Population Cases with disease Controls without disease Exposed Unexposed

9 Odds ratio and corresponding 95% confidence (stratified by age) Analytical Studies 2: Case control study of Hepatitis C seropositivity and lymphoma

10 Design of a cohort study TIME direction of inquiry people exposed disease population without the no disease disease not exposed disease no disease “at risk”

11 Analytical studies 3: Cohort of British Doctors Death by lung cancerCurrent smokerNon smoker Yes a (4,180) b (224) No c (45,820) d (39,776) # at beginning50,000 40,000 Total 90,000

12 Relative risk: risk in exposed/risk in unexposed RR = a  b = .0056 = 14.9 a+c b+d Attributable risk = risk difference = excess risk in smokers = =.078 Cohort of British Doctors cont’d

13 Analytical studies 3: Shanghai - cohort study 18,000 men-synergy (Qian G-S et al, Can Epid Biom. Prev 1194;33) Note: Aflatoxins measured by adducts, interview unreliable

14 Effect Modification (or Interaction) is said to occur when the association between exposure x and outcome y differs by variable z

15 Prevalence of Actinic keratosis in Israeli Dermatologic Patients with and without Psoriasis Psoriatics 409 (89%) 51 (11%) Controls 538 (73%) 200 (27%)

16 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

17 Adjusted odds ratios (OR) for solar keratosis by hair color comparing psoriatics and controls Adjusted for ethnic origin, gender, age and degree of sun exposure

18 Adjusted odds ratios (OR) for solar keratosis by propensity to sunburn comparing psoriatics and controls Adjusted for ethnic origin, gender, age and degree of sun exposure Sometimes

19 Formulating study question Gathering data Hypothesis testing Impact measures The epidemiological tool-box

20 Judging the methodology Kappa statistic & Reliability Life Expectancy – survival analysis, life table analyses The epidemiological tool-box

21 Measurement accuracy N = sample size Outcome Measures Proportional mortality/morbidity The epidemiological tool-box

22 Quality of data (and/or life!) Randomization; Risk – incidence, types of incidence, incidence vs. prevalence, crude vs. disease-specific The epidemiological tool-box

23 Standardization Time Trends Utility assessment Validity Weight of evidence The epidemiological tool-box

24 X-axis Y-axis and plotting the data Z-score and statistical inference Ж - ????? The epidemiological tool-box

25 Steps in Designing and Conducting an Epidemiologic Investigation You have made an observation based on descriptive cancer statistics…….

26 Specify TOPIC and PURPOSE Determining what is KNOWN and UNKNOWN State the CASE FOR ACTION

27 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,

28 Select appropriate STUDY DESIGN Choose & define STUDY VARIABLES Define STUDY POPULATION & SELECTION TECHNIQUES Develop DATA COLLECTION TOOLS

29 PRETEST developed instruments TRAIN FIELD WORKERS CONDUCT/MONITOR FIELD WORK Prepare data for ANALYSIS ANALYSE the data

30 WRITE-UP findings COMMUNICATE findings INCORPORATE results into health planning EVALUATE modified health program

31 It is easier to investigate problems than to solve them. BUT… It’s not so easy to study them either!


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