national multiple family submetering and allocation billing program ...

Table 5.27 Paired samples test, all converted properties
Paired Differences
Estimated Annual Water Use per Unit
Prior to Conversion - Estimated Annual
Water Use per Unit After Conversion
Mean
Difference
Std.
Deviation
Std.
Error
Mean t df
P-
value
4.350 15.902 2.345 1.856 45 0.070
Water savings were also examined by type of billing to which the properties converted.
For submetering, the sample size was quite small (6 properties). The small sample size is not
particularly surprising, since it often expensive to retrofit a property with submeters, and is more
common in new construction. For converted submetered properties, water savings of about 17.5
kgal per unit per year were observed (see Table 5.28).
Table 5.29 shows that the differences from pre-conversion to post-conversion are
statistically significant at the 94% confidence level. In addition, given the small sample size, the
95% confidence interval is quite wide around the submetering conversion water savings
estimate, ranging from –36.1 to +1.1 kgal per unit per year. This is shown in comparison to all
of the converted properties and the RUBS properties in Figure 5.19.
Table 5.28 Estimated water use before and after conversion, submetered properties
Std.
Mean Deviation
Estimated Annual Water Use per Unit Prior to Conversion 68.21 34.24
Estimated Annual Water Use per Unit After Conversion 50.71 20.38
Change in Estimated Annual Water Use Before and After Conversion -17.50 17.67
Percent of Properties That Decreased Annual Water Use per Unit 83.33%
Percent of Properties That Did Not Change Annual Water Use per Unit .00%
Percent of Properties That Increased Annual Water Use per Unit 16.67%
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