EXAM 1 IMPORTANT DEFINITIONS Flashcards
Define sensitvity
Probability that subject D+ tests +ve
Define specificity
Probability D- tests -ve
Define apparent prevalence
Proportion of +ve subjects
Define true prevalence
Proportion of subjects w/ known infection
(D+ total)
Define Positive predictive value
Proportion that subject is T+ and D+
Define Negative predictive value
Proportion that subject is D- and T-
Formula for sensitivity
a/(a+c)
Formula for specificity
d/(b+d)
Formula for apparent prevalence
(a+b)/n
Formula for true prevalence
(a+c)/n
Formula for PPV
a/(a+b)
Formula for NPV
d/(c+d)
List the 5 phases of an epidemic curve
1) endemic level
2) threshold level
3)ascending phase
4)plateau/culminating phase
5) descending phase
Describe the endemic level of an epidemic curve
expected level of disease, high herd immunity, most individuals are carriers, no obvious new carriers, high source of infection
Describe the threshold level
pre-epidemic pd, herd immunity declined
Describe the ascending phase
reduced herd immunity, # of diseased individuals increases, slope depends on pop density and exposure type, high intensity/source of infection
Describe the plateau/culminating phase
depends on availability of susceptible individuals, max # of new cases, herd immunity rises
Describe the descending phase
new cases decreases, herd immunity increases, sick individuals may recover, sensitive individuals die, immunity can happen, infection source decreases
Define cumulative incidence rate
Fraction of initially susceptible individuals in a population who become new cases during a specific follow-up period
Formula for cumulative incidence rate
new cases during a specified period/ avg # individuals at risk
Define cumulative incidence
Indication of avg risk, only for first occurrence of disease
Define incidence density rate
of new cases of disease that occur per unit of individual time at risk in a defined period
Formula for incidence density rate
new cases during specific pd/ sum of person-years at risk periods
crude mortality rate formula
Total # deaths/ avg population
Cause-specific mortality rate
deaths from a particular disease/ avg population at risk during time pd
Formula for proportional mortality rate
Deaths of disease y/ total deaths
Case fatality rate definition
Death among individuals who develop the disease
Formula for case fatality rate
deaths from disease y/ cases of disease y
