| Characteristic | Ionization (n = 366*) (%) | Photoelectric (n = 384*) (%) |
| Respondent | ||
| Female | 64.7 | 63.5 |
| Age (years) | ||
| ⩽24 | 2.6 | 2.3 |
| 25–44 | 42.5 | 38.3 |
| 45–64 | 31.9 | 40.3 |
| ⩾65 | 23.1 | 19.2 |
| Race/ethnicity | ||
| White | 78.2 | 76.2 |
| Asian/Pacific Islander | 10.7 | 11.4 |
| African-American | 3.6 | 5.0 |
| Hispanic | 3.0 | 3.2 |
| Native American | 0.8 | 1.3 |
| Multiracial | 3.0 | 1.3 |
| Other | 0.6 | 1.6 |
| Education | ||
| <High school | 5.2 | 8.7 |
| High school/GED | 21.2 | 25.2 |
| Vocational/technical/some college | 30.0 | 30.5 |
| ⩾College | 43.7 | 35.7 |
| Household | ||
| Number of residents | ||
| 1 | 20.5 | 19.0 |
| 2 | 32.5 | 31.5 |
| 3–4 | 36.9 | 35.7 |
| ⩾5 | 10.1 | 13.8 |
| ⩾1 resident aged | ||
| ⩽4 years | 16.2 | 15.7 |
| ⩽14 years | 33.8 | 35.3 |
| ⩾65 years | 29.0 | 25.5 |
| ⩾1 resident smokes† | 24.4 | 25.0 |
| ⩾1 resident drinks alcohol‡ | 25.9 | 25.3 |
| House | ||
| Single family residence | 98.9 | 100.0 |
| Year built | ||
| ⩽1920 | 9.1 | 11.2 |
| 1921–1940 | 17.8 | 15.2 |
| 1941–1960 | 42.7 | 41.3 |
| 1961–1980 | 22.5 | 21.2 |
| 1981–1996 | 7.9 | 11.2 |
| Ever structurally remodeled | 51.0 | 52.7 |
| Year built or last remodeled | ||
| ⩽1940 | 9.2 | 7.4 |
| 1941–1960 | 27.4 | 22.9 |
| 1961–1980 | 28.4 | 26.3 |
| 1981–2001 | 35.0 | 43.3 |
| Number of floors | ||
| 1 | 39.9 | 40.1 |
| 2 | 47.3 | 48.7 |
| ⩾3 | 12.8 | 11.2 |
| Years in current house | ||
| <1 | 6.6 | 4.2 |
| 1–5 | 31.7 | 29.0 |
| 6–10 | 16.9 | 21.9 |
| ⩾11 | 44.8 | 44.9 |
| Kitchen stove type§ | ||
| Electric | 89.6 | 90.6 |
| Gas | 10.7 | 9.4 |
| Frequency of kitchen stove use | ||
| Daily | 64.5 | 66.6 |
| Multiple days per week | 27.2 | 24.5 |
| Rarely/occasionally/weekends only | 8.3 | 9.0 |
| Main heat source | ||
| Electric | 24.9 | 31.8 |
| Natural gas | 54.4 | 49.2 |
| Oil | 18.8 | 17.4 |
| Wood | 1.7 | 1.3 |
| Other | 0.3 | 0.3 |
| Electric main or secondary heat source | 33.6 | 40.6 |
| Natural gas main or secondary heat source | 53.5 | 49.3 |
| Oil main or secondary heat source | 19.0 | 18.5 |
| Open-element space heater | 19.5 | 20.8 |
| Wood fireplace | 37.5 | 47.1 |
| Gas fireplace insert | 4.9 | 1.8 |
| Wood or pellet stove | 20.8 | 20.8 |
| Frequency of fireplace or stove use¶ | ||
| Daily/weekly | 39.1 | 30.2 |
| Bi-monthly/monthly | 12.1 | 14.3 |
| Rarely/never | 48.8 | 55.5 |
*Among households that were eligible for analyses (had study alarm installed, were home owners, and received a zinc battery in the study alarm).
†Defined as smoking a pack (20 cigarettes) or more per week.
‡Defined as drinking 5 or more alcoholic beverages on occasion.
§Not mutually exclusive since some kitchens have two stoves, so percentages may add to >100%.
¶Based on the single most frequently used fireplace or stove per household.