Public Health Flashcards
Incidence
The number of individuals who develop a condition in a given period of time
Units: % or per 1000
Incidence= No. of new cases during time t/ population at risk
Prevalence
The number of individuals who have a condition at a particular time
Prevalence= No. of existing cases at time t/ total population size
Absolute risk
The risk of developing a condition over a given time period
I.e 1 in 10 at risk of developing cancer
Absolute risk difference
P of case in exposed group- P of case in unexposed group
Relative risk
Ratio of risk in the exposed group to risk in unexposed group
RR= P of case in exposed group/ P of case in unexposed
Normally produces larger value than absolute risk difference
True positive
Number of people who have a disease who were screened as positive
True negative
Number of people who don’t have a disease who were screened as negative
False positive
Number of people who don’t have a disease but were screened as positive
False negative
Number of people who do have a disease but were screened as negative
Sensitivity
The proportion of people with the disease who were correctly identified by the screening test
Sensitivity= True positive/ (true positive + false negative)
Specificity
The proportion of people without the disease correctly identified by the screening test
Specificity= true negative/ (true negative + false positive)
Positive predictive value
The proportion of people with a positive result who have the condition
PPV= True positive/ (true positive + false positive)
Negative predictive value
The proportion of people with a negative result who don’t have the condition
NPV= True negative/ (true negative + false negative)
Cross-sectional study
Prevalence within a population, a snapshot in time.
Exposure Outcome
+ Quick, cheap with few ethical problems and can be used to stimulate further research
- Suffers from selection bias and has no time reference
Case-control study
Comparison of a group of people with a disease and a control group. Can be used to investigate risk factors.
Outcome—> Exposure
+ Quick, cheap and works well for disease with long latent periods
- selection/ information bias and can’t tell incidence