Prevalence rate
Prevalence rate (P)
Number of people with the disease (NPD)
Population at risk (PR)
Incidence rate
Incidence rate (i)
Number of people who fell ill in the period (NPAP)
person-time at risk (PTR)
cumulative incidence rate or risk
cumulative incidence rate or risk (ic)
Number of people who developed the disease in the period (NPDDP)
Number of people without the disease at the beginning of the period. (NPSDIP)
Lethality
Lethality (l)
Number of deaths from a given disease in a given period (NMDDP)
Number of patients from a given disease in the same period (NDDDP)
Relationship between prevalence and incidence
Prevalence (P)
incidence (i)
mean disease duration (DMD)
Detection tests
population (pop)
prevalence (prev)
sensitivity (sens)
specificity (espe)
true positive
vp = pop * prev * sens;
false negative
fn = pop * prev * (1-sens);
false positive
fp = pop * (1-prev) * (1-espe);
true negative
vn = pop * (1-prev) * espe;
prevalence for the positive group
npr = vp / (vp + fp);
prevalence of negative group
nnr = vn / (vn + fn);
