national multiple family submetering and allocation billing program ...

Factors that Influence Water Use
The process of determining the impacts of water billing methods on water use began with
an examination of the factors that may influence water use other than billing method. Using
responses to the manager survey, linked with the cleaned historic billing data provided by each
participating water provider, it was possible to evaluate the significance of a wide variety of
factors on per unit per year water use. Wherever possible these factors were evaluated using
historic billing data from 2001 and 2002. Only factors that were significant at the 95%
confidence level in both years were considered for use in analytic models to evaluate the impacts
of water billing methods.
Categorical Variables
Analysis of Variance (ANOVA) tests were performed to determine which of the nominal
variables from the manager survey is statistically significant in explaining water use. Results
from these analyses are presented in Table 5.12. The mean annual per unit water use (in kgal)
for each set of property factors is shown along with the standard deviation (kgal) and the sample
size. The p-value comes from the ANOVA test. Factors with p-values less than 0.05 were
considered “statistically significant,” meaning that if there were no difference, the probability of
seeing a result as or more extreme than that seen in the sample was less than 5%. Only factors
with a p-value of 0.05 or less in both 2001 and 2002 were selected for use in the multiple linear
regression models. The factors in Table 5.12 are sorted by order of statistical significance with
the most significant factors listed first. The dark line indicates the break point for factors
selected for inclusion in advanced regression models.
Statistically significant categorical variables that were associated with per unit indoor
water use in this sample of multi-family properties included:
! Year property was built (1994 or earlier, 1995 or later)
! Whether the property was a senior citizen/retirement community
! Presence of a swimming pool
! Low-flow (LF) faucet aerators
! ULF toilets
! Washing machine replacement
! Presence of a play area
! Presence of basketball court
! Presence of cooling tower
! Presence of food service facility or restaurant
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