national multiple family submetering and allocation billing program ...

In Table 5.24 the P-value is shown for the difference in water usage between the
submetered and in-rent matched properties along with the 95% confidence interval around this
estimate. Using a dependent t-test, the difference in annual water use per unit was statistically
significant (p=0.046). The 95% confidence interval around the water savings suggests that the
difference in water use is likely to range from -0.2 to -19.7 kgal per unit per year in submetered
properties compared to in-rent properties. Similarly, a statistically significant savings was found
for RUBS (p=0.008), as shown in Table 5.25. This is the only analysis from the data collected
for this Study in which such a finding was observed. As mentioned previously and discussed
below, it appears the sample drawn for the RUBS/in-rent matched pair analysis was not
representative of the entire manager survey sample.
Table 5.24 Average water use (kgal/unit/year) difference, submetered/in-rent pairs
95% Confidence
Interval for Mean
Mean Difference Std. Error P-value Difference
Lower
Bound
Upper
Bound
In-Rent compared to
Submetered
-9.980 4.684 0.046 -19.750 -0.210
Table 5.25 Average water use (kgal/unit/year) difference, RUBS/in-rent pairs
95% Confidence
Interval for Mean
Mean Difference Std. Error P-value Difference
Lower
Bound
Upper
Bound
In-Rent compared to
RUBS
-18.387 5.890 0.008 -31.112 -5.662
Four types of comparisons were included in this study (large sample from post card
survey of managers; medium sample from mailed survey of managers; small sample of pre-post;
and small sample of matched pairs), where each level intended to control better the differences in
property characteristics that could subvert conclusions about billing type as the variable
responsible for observed differences in water usage. If all levels of the study supported each
other, conclusions would be strongest. Where three of the four levels are mutually supportive,
but one is not, then one must examine the anomalous finding. In this study, the matched pair
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