Transportation Statistics and Microsimulation

282    ◾    Transportation Statistics and Microsimulation

Example 14.6 (Example 14.4 continued)

Researchers desire to find an interval that is believed to contain the free-flow

mean speed at some probability level. Say that they wish to obtain a 95%

credible interval for µ. Because the standard deviation of speeds is known to

be σ = 6 in this case, the formula in Equation 14.17 can be used to obtain the

credible interval. Recall that the posterior mean and posterior standard devia-

tion were E(μ|x

–

) = 49.44 and Std(μ|x

–

) = 2, respectively, from Examples 14.2 and

14.4. By plugging in those values as well as z

1–α/2

= 1.96 in Equation 14.