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national multiple family submetering and allocation billing program ...

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Comparison of the Manager Survey Respondents with the Postcard Survey Respondents<br />

The manager survey was sent to in-rent <strong>and</strong> impact properties identified through the<br />

postcard survey. In addition, impact properties identified by <strong>billing</strong> service companies <strong>and</strong> from<br />

web sources that had not responded to the postcard survey were also included in the manager<br />

survey. Since a lower percentage of impact properties were identified than originally anticipated,<br />

a saturation sampling technique was chosen for the manager survey so that every identified<br />

impact property received a manager survey. The sample of in-rent properties was selected using<br />

a stratified r<strong>and</strong>om sampling methodology described earlier in this chapter.<br />

Quality assurance tests were conducted on entire group of respondents <strong>and</strong> on the sample<br />

of properties from each study site that returned the manager survey to determine whether the<br />

water use characteristics of the manger survey respondents (sample) were statistically similar to<br />

the multi-<strong>family</strong> properties that responded to the postcard survey (population). To compare the<br />

respondents with the population, statistical tests were used to determine whether statistically<br />

significant differences existed in water use characteristics among the two groups.<br />

A series of t-tests were conducted at a 95 percent confidence level to determine if there<br />

was a statistically significant difference in the mean annual water use of manager survey<br />

respondents versus the population. The results can be seen in Table 3.8. The most important<br />

comparison evaluated 2001 water use for the postcard respondents (n=7,319) with 2001 water<br />

use for the manager survey respondents (n=1,157). The water use in these two groups was found<br />

to be statistically different at a 95% confidence level, with a 2.09 kgal higher estimate for<br />

postcard survey respondents (53.54) compared to manager survey respondents (51.45). A<br />

similar difference was observed among the in-rent properties, but not among the impact<br />

properties. This may be due to manner in properties were sampled for the manager survey. All<br />

impact properties were selected, but in-rent properties were selected within strata based on the<br />

number of units per property, to allow the in-rent properties to more closely resemble the impact<br />

properties, which tended to be larger (more units per property) than in-rent properties.<br />

This means that on the basis of water use alone the manager survey respondents were not<br />

statistically different from postcard survey respondents which in turn were determined to be<br />

representative of the population of multi-<strong>family</strong> homes found in these 13 study sites.<br />

52

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