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Epidemiology: a very basic start….

Epidemiology: a very basic start…. Gavin Shaddick Department of Mathematical Sciences University of Bath UBC, September 2008. What is epidemiology?. “The study of skin diseases?”. What is epidemiology?. “The study of skin diseases?”

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Epidemiology: a very basic start….

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  1. Epidemiology: a very basic start…. Gavin Shaddick Department of Mathematical Sciences University of Bath UBC, September 2008

  2. What is epidemiology? • “The study of skin diseases?”

  3. What is epidemiology? • “The study of skin diseases?” • “The study of the distribution and determinants of health-related states in specified populations, and the application of this study to control health problems."

  4. The early days…John Snow and the Broad Street Pub

  5. The early days…John Snow and the Broad Street Pump

  6. Number of cholera cases in proximity to water pump, 1854

  7. Overview of epidemiological framework • Incidence • Proportion of people who develop the disease during specified period • Risk • Probability of developing disease within a specified time interval (between 0 and 1) • Relative Risk • The ratio of risks under two exposure distributions

  8. Relative risks and confidence intervals • RR is a ratio • Values ‘significantly’ >1 indicate increase in risk with increased exposure • Values ‘significantly’ <1 indicate protective effect of exposure • Values ‘close’ to 1 indicate no significant effect • 95% confidence interval • Gives a range of values within which we are ‘confident’ the true relative risk lies • Interest in values with the lower limit greater than one

  9. RR = 1.3 1.5 1.1 0.9 1.7 Confidence intervals • 95% confidence interval • Gives a range of values within which we are ‘confident’ the true relative risk lies • Interest in values with the lower limit greater than one 1

  10. Temporal relationships between exposure and effect Latent Acute Lead time Latency Time Time Exposure and Effect Chronic Endemic Time Time

  11. SIRs for (a) lung and (b) brain cancer in North-West England, 1991-91

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