Case Study:

San Francisco Bay Area, California

Methodology

Comparison Between Groups

In addition to simply looking at differences in accessibility, MTC conducted statistical tests to determine whether these differences were significant. The tests used in this analysis include paired t-tests and the standard error of difference between means.

The paired t-test is used to compare the project with the no-project alternative. This test examines, on a zone pair basis, whether the difference between the project and no-project accessibility measure is significantly greater than zero. If the t-statistic on a paired t-test is greater than 1.96, then there is at least a 95 percent probability that there is a difference between the two alternatives.

The standard error of difference between means is used to compare accessibility between "disadvantaged" and "non-disadvantaged" sets of TAZs. The difference between means is divided by this standard error of difference between means to obtain a t-statistic. If the t-statistic is greater than 1.96, then it is concluded that there is a significant difference (or, there is less than a one-in-20 probability that there is no difference between disadvantaged and advantaged neighborhoods).

Percent differences are also reported in the analysis. These are fairly intuitive measures to describe the magnitude of differences between alternatives and between subsets of neighborhoods.

[TOP]