3方差的专业定义是随机变量的二次中心矩，与期望值之差的平方的加权平均值。
The technical definition of variance is the random variable's second central moment, the weighted average of the square of the differences from the expected value.
在第一种模型中，假定出行者的广义出行费用定义为平均行程时间和行程时间均方差的线性加权和，同时出行者能够正确认识自己的广义出行费用。
In the first model users' generalized travel cost are assumed to be weighted sum of the standard deviation and the mean travel time, and users have perfect knowledge of the road network condition.
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