national multiple family submetering and allocation billing program ...

Figure 5.1 shows the frequency distribution of water use for each of these four groups,
using the combined 2001-2002 historic billing data. These histograms are plotted as lines rather
than bars to make it easier to compare the shape of each distribution. The in-rent, submetered,
and RUBS frequency distributions are quite similar in shape with the RUBS curve slightly
elevated in the 60 – 90 kgal/unit/year range. The hot water hybrid distribution appears to be
markedly shifted to the left (suggesting lower water use), but higher use in the 70 – 110
kgal/unit/year range pushed the average up.
25%
20%
Relative Frequency
15%
10%
5%
0%
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
Avg. Annual Water Use Per Unit (kgal)
In-Rent Submetered RUBS Hot Water Hybrid
Figure 5.1 Frequency distribution, avg. annual water use per unit, postcard survey
respondents
Three separate t-tests were performed comparing the annual per unit water use (2001 and
2002) from the in-rent properties first against the submetered properties, then the RUBS
properties, and finally the hot water hybrid properties. The purpose of these analyses was to
determine if a statistically significant difference in water use exists between any of these groups
at the 95% confidence level. The results of these t-tests are shown in Table 5.7. The null
hypothesis in each test was that the difference in mean water use was 0. The alpha-level for a
95% confidence level was 0.05. Only the difference in means between the in-rent and the
submetered properties proved to be statistically significant at the 95% confidence level. There
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