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Public HealtH ScienceS ` PUBLIC HEALTH SCIENCES—EPIdEmIoLogy ANd BIoSTATISTICS Public HealtH ScienceS ` PUBLIC HEALTH SCIENCES—EPIdEmIoLogy ANd BIoSTATISTICS SectiOn ii 259
Incidence vs Incidence = # of new cases (per unit of time) Incidence looks at new cases (incidents).
prevalence # of people at risk
# of existing cases (at a point in Prevalence looks at all current cases.
Recurrence Prevalence =
Total # of people time)
Incidence
in a population
Prevalence Prevalence = average duration
Incidence rate ×
1 – prevalence of disease
Mortality Cure
Prevalence ≈ incidence for short duration disease Prevalence ∼ pretest probability.
(eg, common cold). prevalence PPV and NPV.
Prevalence > incidence for chronic diseases, due to
large # of existing cases (eg, diabetes).
SITUATIoN INCIdENCE PREVALENCE
survival time —
mortality —
Faster recovery time —
Extensive vaccine administration
risk factors
Precision vs accuracy
Precision (reliability) The consistency and reproducibility of a test. Random error precision in a test.
The absence of random variation in a test. precision standard deviation.
precision statistical power (1 − β).
Accuracy (validity) The closeness of test results to the true values. Systematic error accuracy in a test.
The absence of systematic error or bias in a test.
Accuracy Accuracy
High Low High Low
High High Low Low
Precision Precision
FAS1_2019_06-PubHealth.indd 259 11/7/19 4:16 PM
