**6. Household preferences for plumbing material**

### **6.1 Summary of descriptive results**

Every respondent to the first Southeastern Community survey was asked to participate in the follow-up survey. Three hundred sixty three respondents agreed to participate, and 245 responded to the follow-up survey. Each respondent evaluated three Conjoint Analysis

Households' Preferences for Plumbing Materials 435

For this part of the analysis, the Ordered Logit regression is utilized in the plumbing material estimation of preferences and is estimated at the aggregate response level. The aggregate level analysis implies that average value coefficients are estimated for the

The analysis provides information on the preferences of homeowners for plumbing materials, and the attributes that drive their decision, when making purchasing decision with regards to the type of home plumbing system. Each respondent evaluated a set of two plumbing material portfolios at one time for a total of six portfolios using the valuation metrics 1-9 described earlier. Each of the plumbing materials has a set of attributes described in Table 1. Each material attribute level is employed as the independent variable in the material preference analysis. They are coded as dummy variables taking a value of 1 when that plumbing material characteristic is a part of the product portfolio and zero otherwise. Finally, the socioeconomic characteristics (reported in the first survey) are also included in the Ordered Logit model. These characteristics represent household home value (continuous variables), age of the house (continuous variable), plumbing material type (dummy variable), pinhole leak occurrences in the past (dummy variable), and respondent's previous

The first step in evaluating the results of the Ordered Logit model is to review the model performance / fitting criteria. The model fitting information indicates the parameters for which the model-fit is calculated. There are four variables that evaluate the goodness of fit: Chi-square statistics4, p-value5, log-likelihood value6, and R-square7. The model fitting

3 Variables for race, education level, and gender were not included in the model, as little variation in these characteristics was observed for the sample of respondents. 4 Chi-square Test establishes whether or not an observed frequency distribution differs from a

5 P-value is the probability of obtaining a test statistic at least as extreme as the one that was actually

6 Log-likelihood Test compares the fit of two models, one of which (the null model) is a special case of

7 R-square represents the proportion of variability in a data set that is accounted for by the statistical

Plumbing Material Frequency Percent Material A 116 50.4 Material B 48 20.8 Material C 41 17.8 Neither 4 1.7 Missing 22 9.7 Total 230 100

Table 9. Plumbing material chosen as most preferred.

**6.2.1 Order logit model without socioeconomics variables** 

cost of plumbing material repairs and replacement (continuous variable).3

**6.2 Empirical analysis results** 

participating sample of respondents.

theoretical distribution (Aaron, 2005).

model (Aaron, 2005).

the other (the alternative model) (Aaron, 2005).

observed, assuming that the null hypothesis is true (Aaron, 2005).

scenarios describing a set of two plumbing materials (Material A= epoxy coating, Material B = plastic, and Material C = copper that were blinded to avoid survey exposure bias) and answered questions comparing material attributes. Each plumbing material was described by the following attributes: corrosion resistance, taste and odor, health effects, convenience of installation, proven performance on the market, plumbing material cost, and warranty length. Table 1 presents the plumbing material attributes in more detail.

Each respondent was asked to compare a pair of plumbing materials, and evaluate each plumbing material based on a 1-9 preference scale. For example, Material A might be rated as 6, while Material B might be rated as 1. The 1-9 preference scale had a verbal preference assigned to each categorical value. Preference values of 1, 3, 5, 7, and 9 were assigned to 'Not Preferred', 'Moderately Preferred', 'Strongly Preferred', 'Very Strongly Preferred', and 'Extremely Preferred', respectively. Two hundred thirty respondents fully answered all questions, and each viewed three pairs of two plumbing materials resulting in 1,380 preference responses.

As each presented plumbing material had all attributes listed, and there was no randomization of attribute levels across the plumbing materials, the preference score was easily identified with the preferred plumbing material by comparing the attribute levels with the plumbing material descriptions. All preference responses to each plumbing material were then summed, and the plumbing material with the highest number of 'Extremely Preferred' responses and with lowest number of 'Not Preferred' responses was selected as the most preferred plumbing material. Table 8 presents the descriptive statistical summary of preference valuation break down of the 1,380 responses for plumbing materials. Material C (copper) is the least preferred type of plumbing material (211 not preferred responses), while Material A (epoxy coating) is the most preferred material among homeowners (39 extremely preferred responses).


Table 8. Preference valuation of plumbing materials.

In addition to evaluating three sets of two plumbing material scenarios, each respondent selected the most preferred plumbing material across all three materials displayed at the same time. Table 9 presents that Material A (epoxy coating) is chosen as the preferred plumbing material by more than 50% of respondents. Material C (copper) is the least often chosen as the preferred plumbing material (17.8%). These two separate measures yield the same result of Material A being the most preferred plumbing material across the three alternatives.

scenarios describing a set of two plumbing materials (Material A= epoxy coating, Material B = plastic, and Material C = copper that were blinded to avoid survey exposure bias) and answered questions comparing material attributes. Each plumbing material was described by the following attributes: corrosion resistance, taste and odor, health effects, convenience of installation, proven performance on the market, plumbing material cost, and warranty

Each respondent was asked to compare a pair of plumbing materials, and evaluate each plumbing material based on a 1-9 preference scale. For example, Material A might be rated as 6, while Material B might be rated as 1. The 1-9 preference scale had a verbal preference assigned to each categorical value. Preference values of 1, 3, 5, 7, and 9 were assigned to 'Not Preferred', 'Moderately Preferred', 'Strongly Preferred', 'Very Strongly Preferred', and 'Extremely Preferred', respectively. Two hundred thirty respondents fully answered all questions, and each viewed three pairs of two plumbing materials resulting in 1,380

As each presented plumbing material had all attributes listed, and there was no randomization of attribute levels across the plumbing materials, the preference score was easily identified with the preferred plumbing material by comparing the attribute levels with the plumbing material descriptions. All preference responses to each plumbing material were then summed, and the plumbing material with the highest number of 'Extremely Preferred' responses and with lowest number of 'Not Preferred' responses was selected as the most preferred plumbing material. Table 8 presents the descriptive statistical summary of preference valuation break down of the 1,380 responses for plumbing materials. Material C (copper) is the least preferred type of plumbing material (211 not preferred responses), while Material A (epoxy coating) is the most preferred material among

Preference Response Value

In addition to evaluating three sets of two plumbing material scenarios, each respondent selected the most preferred plumbing material across all three materials displayed at the same time. Table 9 presents that Material A (epoxy coating) is chosen as the preferred plumbing material by more than 50% of respondents. Material C (copper) is the least often chosen as the preferred plumbing material (17.8%). These two separate measures yield the same result of Material A being the most preferred plumbing material across the three

Material A 103 134 99 85 39 Material B 148 151 85 56 20 Material C 211 156 56 31 8 Total 460 441 240 172 67

Strongly Preferred

Very Strongly Preferred Extremely Preferred

Moderately Preferred

length. Table 1 presents the plumbing material attributes in more detail.

preference responses.

Plumbing Material

alternatives.

homeowners (39 extremely preferred responses).

Not Preferred

Table 8. Preference valuation of plumbing materials.


Table 9. Plumbing material chosen as most preferred.
