Transportation Statistics and Microsimulation

Common Probability Distributions    ◾    75

Note: The normal distribution is often written in short form as N(μ,σ

2

). For

example, N (10, 2) would imply that a variable is distributed normally with

a mean of ten units and a variance of two units. However, some authors

use the short form N(μ,σ). Therefore, it is critical that the engineer under-

stands the format a particular author is using so he or she knows whether

the second parameter is variance or standard deviation.

Both the variance and standard deviation, σ, are indicators of spread.

For the normal distribution, the latter is more oen used as a measure of

spread because of some specia ...