
18 Ergonomics in the Automotive Design Process
Thus, the mean ( μ) and standard deviation (σ) are the two parameters of the normal distribution (i.e.,
they dene the location and spread of the distribution, respectively).
The cumulative distribution of f(x) is denoted as F(x) and is dened as follows:
F x f x x x
x
x
x
( ) ( )d
( ) /
= =
−∞
− −
−∞
∫ ∫
1
2
2 2
2
m s
e d
Since the normal distribution is symmetrical about mean, F(x) = 0.5 denes the 50th percentile
value. Thus, the 50th percentile value equals the mean (μ).
Percentile values are used to evaluate accommodation with respect to a given variable (x)
(i.e.,what percentage of the population ...