Screening is the application of a test to asymptomatic individuals to assess the likelihood that an individual has a particular disease.
Surveillance of disease is used to look for changes in trends or distribution of the disease.
Prevalence = Prevalencestart + Incidence Time
(when population and disorder stable)
A risk factor is an exposure or attribute that increases the probability of a disease.
Disease | No Disease | |
---|---|---|
Exposure | a | b |
No Exposure | c | d |
The absolute risk is always between zero and 1 and the relative risk is always larger than zero.
Absolute Risk Exposed Individuals:
Absolute Risk Non Exposed Individuals:
Relative Risk:
The relative risk is the risk of developing the disease that is due to an exposure in the exposed group
Odds Ratio:
The odds ratio is the ratio of the odds of a disease occurring among exposed individuals to that of it occurring in unexposed individuals.
An odds ratio or relative risk greater than 1 indicates the exposure is a risk factor for developing the disease. If the odds ratio or relative risk is 1, the exposure has no effect on the disease; if they are less than 1, the exposure protects against disease.
In R / JGR console 1:
library(epiR)
mat<-matrix(c(a,c,b,d),ncol=2) {enter values!}
mat
[,1] [,2]
[1,] a b
[2,] c d
epi.2by2(mat)
Outcome + Outcome – Total Inc risk * Odds
Exposed +
Exposed –
Total
Point estimates and 95 % CIs:
———————————————————
Inc risk ratio
Odds ratio
Attrib risk *
Attrib risk in population *
Attrib fraction in exposed (%)
Attrib fraction in population (%)
———————————————————
* Cases per 100 population units
The package epiR 1 should be installed.
The odds ratio provided is the maximum likelihood estimate that is different from the cross product ratio. To obtain the cross product ratio :
summary(epi.tests(mat))
est lower upper
aprev
tprev
se
sp
diag.acc
diag.or {This is the cross product (diagnostic) odds ratio}
nnd
youden
ppv
npv
plr
nlr