epidemiological principles Flashcards
what is a case control study
known outcome
compare individuals with/without outcome and determines what connects them
How would you design a case control study
retrospective
exposure associated with outcome
identify cases and controls
look back to see who was exposed
advantages of a case control study
cheap, quick, good for outbreaks of disease
What is prevalence
the frequency of a disease in a population at a point in time new and pre-existing cases number cases/number people useful for planning measures burden of disease compare burden
What is incidence
the number of new infections within a population over time
How do you estimate incidence
define time period
define population
accurate test to define true case - easier for infections with a short time period
How does incidence influence policy makers eg ebola
when incidence = 0
outbreak over
reopen schools etc
what is mortality
number of deaths from a disease in a population over a given time
= deaths in time period/population at start of time period
explain the relationship between prevalence and mortality
define prevalence and mortality
mortality falls, prevalence increases
How can incidence decrease but prevalence increase in HIV
Antiretroviral therapy improves survival, prevalence increases
reduce transmission
fewer new people infected
Example of how prevalence can be measured
Blood/saliva testing ELISA
self-report
Problems with measuring prevalence
‘point prevalence’ need to consider whose data was and wasn’t available on census day- participation bias
self-reporting errors
sensitivity - positives/true positives
specificity - -ve/true -ve
How do you calculate incidence
overall = no new cases/total number in cohort
better overall = no new cases/ -ves + .5*new cases
this shows how many people infected half way through the year
