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?” “The study of the distribution and determinants of health-related states in specified populations, and the application of this study to control health problems."

The early days…John Snow and the Broad Street Pub

The early days…John Snow and the Broad Street Pump

Number of cholera cases in proximity to water pump, 1854

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

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

Confidence intervals 95% confidence interval95% 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 RR =

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

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