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The epidemiological tool-box

The epidemiological tool-box. A ssociations – quantification using rate ratios, rate differences, odds ratios. Analytical epidemiology 1: Ecological Studies. The association between quantity of salt sold and oesophageal cancer mortality in counties of Henan province, China.

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The epidemiological tool-box

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  1. The epidemiological tool-box • Associations – quantification using rate ratios, rate differences, odds ratios

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

  3. Prevalence of carriers of hepatitis B surface antigen

  4. Risk for cancer of the liver (cases/100000 population in areas of high risk for this cancer - sub Saharan Africa and eastern Asia

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

  6. 2*2if only life were so simple…

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

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

  9. 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”

  10. 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 beginning 50,000 40,000 Total 90,000

  11. Cohort of British Doctors cont’d 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

  12. 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

  13. Effect Modification (or Interaction) is said to occur when the association between exposurex and outcomey differs by variablez

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

  15. 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

  16. 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

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

  18. The epidemiological tool-box • Formulating study question • Gathering data • Hypothesistesting • Impact measures

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

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

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

  22. The epidemiological tool-box • Standardization • Time Trends • Utility assessment • Validity • Weight of evidence

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

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

  25. Specify TOPIC and PURPOSE • Determining what is KNOWN and UNKNOWN • State the CASE FOR ACTION

  26. 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

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

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

  29. WRITE-UP findings • COMMUNICATE findings • INCORPORATE results into health planning • EVALUATE modified health program

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

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