| Independent Variables (Demographic/Home Characteristic) |
| Nominal Level |
| Sex |
Two categories |
z-test for difference of proportions to test difference between phone and Web respondents in each category, including “don’t know” or “prefer not to answer.” |
| Race or identity |
Five categories |
| Employment status |
Seven categories |
| Homeownership |
Two categories |
| Home type |
Eight categories |
Not included in analyses |
| Home heating type |
Three categories |
| Water heating type |
Three categories |
| Ordinal Level |
| Age |
Ordinal, eight levels |
Mann-Whitney U to test the difference between phone and Web respondents in the distribution of responses across all levels.
z-test for difference of proportions to test difference between phone and Web respondents in “don’t know” or “prefer not to answer.” |
| Household income |
Ordinal, ten levels |
| Education |
Ordinal, four levels |
| Home size |
Ordinal, six levels |
| Household size |
Ordinal, seven levels |
| Home age |
Ordinal, eight levels |
Not included in analyses |
| Dependent Variable (Item Nonresponse) |
| Item nonresponse level |
Dichotomous, respondents with at least one “don’t know” or “prefer not to answer” response to up to 13 demographic questions and up to 12 program indicator questions. |
z-test for difference in mean percentage nonresponse between phone and Web respondents. |