The Impact of Wind Power Projects on Residential Property Values ...

Figure 11: Sales Volumes by PERIOD and DISTANCE
Percentage<strong>of</strong>HomesThatSoldOfThoseAvailabletoSell
6.0%
5.5%
5.0%
4.5%
4.0%
3.5%
3.0%
2.5%
2.0%
1.5%
1.0%
0.5%
0.0%
Less Than
3 Years
Before
Announcement
After
Announcement
Before
Construction
Inside One Mile
Between One and Three Miles
Between Three and Five Miles
Less Than
2 Years
After
Construction
Between
2 and 4 Years
After
Construction
7.2. Model Form
To investigate whether the rate <strong>of</strong> sales transactions is measurably affected by the wind facilities,
the various resulting sales volumes shown above in Table 29 and Figure 11 are compared using a
t-Test, as follows:
t
(x1
x 2)
s
n
s
n
2 2
1 2
1 2
where
xandx 1 2 are the mean sales volumes from the two categories being compared,
2 2
s1 and s
2
are variances <strong>of</strong> the sales volumes from the two categories being compared, and
n1and n
2
are numbers <strong>of</strong> representative volumes in the two categories. 100
<strong>The</strong> degrees <strong>of</strong> freedom used to calculate the p-value <strong>of</strong> the t statistic equals the lower <strong>of</strong> (n 1 – 1)
or (n 2 – 1).
Three sets <strong>of</strong> t-Tests are conducted. First, to test whether sales volumes have changed with time
and are correlated with wind facility construction, the volumes for each DISTANCE group in
later periods (x 1 ) are compared to the volume in that same group in the pre-announcement period
(x 2 ). Second, to test whether sales volumes are impacted by distance to the nearest wind turbine,
the volumes for each PERIOD group at distances closer to the turbines (x 1 ) are compared to the
volume in that same group in the three to five mile distance band (x 2 ). Finally, for reasons that
will become obvious later, the sales volumes for each PERIOD group at distances within one
(12)
100 <strong>The</strong> number <strong>of</strong> representative volumes could differ between the two categories. For instance, the “less than three
years before announcement” category represents three years – and therefore three volumes – for each study area for
each distance band, while the “less than two years after construction” category represents two years – and therefore
two volumes – for each study area for each distance band.
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