Base Rate (Population)

Definition

The population prevalence of a variable of interest is known as the base rate.

Current Knowledge

Base rates can be calculated using the following formula (Gouvier 1999):

$$ \mathrm{Base}\ \mathrm{rate}=\#\mathrm{cases}\ \mathrm{with}\ \mathrm{condition}\ \mathrm{of}\ \mathrm{in}\mathrm{terest}/\#\mathrm{cases}\ \mathrm{in}\ \mathrm{a}\ \mathrm{population} $$

In neuropsychological settings, base rates are often used to characterize diagnostic accuracy and interpret the sensitivity and specificity of a clinical assessment. The sensitivity of a test is the probability of correctly identifying an individual with impaired functioning as actually being impaired, while the specificity of a test is the probability of correctly identifying an individual with normal functioning as actually being normal (Lezak et al. 2012). When the base rates of a condition are low, the sensitivity of a test may be misleading. When the base rates of a condition are high, the specificity of a test may...