Assessing Dynamic Exposure to Air Pollution - Space-Time Integration in Geography and GIScience - page 289

16.5 Results

To examine whether there are significant differences between static and dynamic
exposures for the subsample as a whole and for various subgroups, the 292
individuals in the subsample were grouped into different gender, income, education,
and age groups. First, participants' age was categorized into three groups: young
(19-40), middle (41-61), and old (62-83) age groups. These age categories were
derived based on the range and distribution of the youngest and oldest individuals in
the subsample. The nine income groups in the original dataset were re-classified into
three categories: low, middle, and high income groups. Lastly, the six categories of
education in the original dataset were reclassified into three groups: less than high
school/high school, vocational/some college, and undergraduate/graduate.
Using these groupings, several paired t-tests were performed to examine whether
there are significant differences between static and dynamic exposures to particulate
matter. Paired t-tests were used because two different exposure measures for the
same individual were compared and they were thus not independent of each other.
As shown in Table 16.1 , the results indicate that, for the entire subsample of 292
individuals, static exposures (231.05 g/m 3 ) were basically the same as dynamic
exposures (229.89 g/m 3 ). The small difference of 1.16 g/m 3 was not statistically
significantly (p D 0.57).
As Table 16.1 also shows, there are no significant differences between static
and dynamic exposures for all gender, income, education, and age subgroups in
the subsample. These differences range from 0.59 g/m 3 (high school or below) to
9.94 g/m3 (low income). These results suggest that taking into account of people's
out-of-home activities and trips did not seem to make a difference in the level
of exposure they experienced - as also indicated by the high Pearson correlation
coefficients (from 0.82 to 0.96) between the static and dynamic exposures for

Table 16.1 Static and dynamic exposures to air pollution

Static exposure
(g/m 3 )

Dynamic
exposure (g/m 3 )

Mean
difference

Paired t-test
p-value

Pearson
correlation

All individuals (292) 231.05 229.89 1.16 0.57 0.88

Men 231.05 229.30 1.75 0.55 0.87

Women 231.05 230.49 0.56 0.84 0.89

Low income 237.81 247.74 9.94 0.21 0.86

Middle income 242.21 239.37 3.84 0.21 0.89

High income 223.34 221.55 1.79 0.56 0.88

High school or below 232.34 232.93 0.59 0.84 0.96

Vocational/some college 223.64 224.56 0.92 0.76 0.93

Undergraduate/graduate 235.75 233.08 2.67 0.44 0.83

Young 237.56 237.71 0.15 0.97 0.89

Middle age 226.26 223.41 2.85 0.37 0.82

Old 235.18 234.40 0.78 0.84 0.94