Transportation Spending by Low-Income California Households ...

Appendix A
General Information on Methods
Details on the Methods Used to Define the Income
Groups
The income groups we created across the four datasets are built on
the federal poverty thresholds, which account for the size of the family
and the number of children present. 1 Generally speaking, we use
household characteristics to group the data into those below the poverty
level (poor), those below 200 percent of the poverty level (low-income),
and those at or above 200 percent of the poverty level (higher-income).
PUMS data show that the poor group accounts for the poorest 11
percent of the metropolitan California population; the low-income
group accounts for the poorest 27 percent; and the higher-income group
accounts for the top 73 percent of the income distribution.
Because the data available on the four datasets varied widely, we were
not able to use precisely the same definitions for each, rather, we used the
methods described below to approximate similar groupings across the
four datasets. The table below summarizes the cutoff points we used to
designate our poor, low-income, and higher-income groups, and further
details are provided in the text.
We use the poverty status variable available in the PUMS data to
categorize households or workers into the three income categories. The
PUMS poverty status variable incorporates the structure of the official
poverty thresholds, based on family income and family structure. The
value of the poverty status variable ranges from 1 to 501, with 1
indicating that income constitutes 1 percent of the poverty threshold for
that household, and 501 indicating that income constitutes more than
500 percent of the poverty level. Therefore, a person or household with
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1 The official poverty thresholds can be found at http://www.census.gov/hhes/
poverty/threshld.html.
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