Study of disease in populations

(1) Basic epidemiology

• Need for denominators, person time at risk

• Measures of disease frequency (prevalence/incidence)

• Measures of effect (relative [RR, OR, RR] and difference [risk/rate difference] measures)

(2) Basic statistics

• Continuous and categorical variables

• Descriptive statistics

• Statistical tests of association

• p values and confidence intervals

• OR, RR

• Controlling for confounding: logistic regression

• Sample size and power

(3/4) Study design

• Describe major study designs used in epidemiological research:

• Strengths and weakness of different designs

• Exposures, outcomes, other exposures (potential confounders)

(5/6) Is this test any good?

Learning objectives

• Define and calculate sensitivity, specificity, PPV, NPV

• Describe the relationship between prevalence and predictive values

• Describe accuracy and likelihood ratios as alternative methods of evaluating a diagnostic test

Notes

• Sensitivity (% of positive test results in people with a disease): important for screening tests. The test is "sensitive" i.e. good at identifying people with the disease

• Specificity (% of negative results in people without the disease): important as definitive tests (e.g. HIV). The test is "specific" for the disease, or "not-specific" (e.g. syndromic approach to vaginal discharge

• Predictive value: % of positive/negative results that are true positive/negative (depends on sensitivity/specificity of the test & the prevalence of disease in the population)

• Likelihood ratio (alternative way of describing test performance): probability of disease after a positive or negative test result (e.g. LR+=sensitivity/1-specificity)

(7/8) How to read a paper

• Critically appraise a published paper

• Evaluate the relevance of a published paper to your clinical practice or work

(9/10) Study design practical

• To develop an appropriate study design for the investigation of a real problem

• To put into practice the methods discussed in the study design lecture

(11/12) Systematic review

(13/14) Outbreak

• Basic principles of an outbreak investigation

• Infectious diseases epidemiology and modelling