A housing unit is owner occupied if the owner or co-owner lives in the unit even if it is mortgaged or not fully paid for. The owner or co-owner must live in the unit and usually is Person 1 on the questionnaire. The unit is "Owned by you or someone in this household with a mortgage or loan" if it is being purchased with a mortgage or some other debt arrangement, such as a deed of trust, trust deed, contract to purchase, land contract, or purchase agreement. The unit is also considered owned with a mortgage if it is built on leased land and there is a mortgage on the unit. Mobile homes occupied by owners with installment loans balances are also included in this category.

A housing unit is "Owned by you or someone in this household free and clear (without a mortgage or loan)" if there is no mortgage or other similar debt on the house, apartment, or mobile home including units built on leased land if the unit is owned outright without a mortgage.

The tenure item on the Census 2000 questionnaire distinguishes between units owned with a mortgage or loan and those owned free and clear. In the sample data products, as in the 100-percent products, the tenure item provides data for total owner-occupied units. Detailed information that identifies mortgaged and nonmortgaged units are provided in other sample housing matrices. (For more information, see discussion under "Mortgage Status," "Selected Monthly Owner Costs," and "Selected Monthly Owner Costs as a Percentage of Household Income in 1999.")

All occupied housing units that are not owner occupied, whether they are rented for cash rent or occupied without payment of cash rent, are classified as renter occupied. "No cash rent" units are separately identified in the rent tabulations. Such units are generally provided free by friends or relatives or in exchange for services, such as resident manager, caretaker, minister, or tenant farmer. Housing units on military bases also are classified in the "No cash rent" category. "Rented for cash rent" includes units in continuing care, sometimes called life care arrangements. These arrangements usually involve a contract between one or more individuals and a service provider guaranteeing the individual shelter, usually a house or apartment, and services, such as meals or transportation to shopping or recreation. (For more information, see "Meals Included in Rent.")

Data on tenure have been collected since 1890. For 1990, the response categories were expanded to allow the respondent to report whether the unit was owned with a mortgage or loan, or free and clear (without a mortgage). The distinction between units owned with a mortgage and units owned free and clear was added in 1990 to improve the count of owner-occupied units. Research after the 1980 census indicated some respondents did not consider their units owned if they had a mortgage. In Census 2000, we continued with the same tenure categories used in the 1990 census.

This measure divides the rooms distribution into two equal parts, one-half of the cases falling below the median number of rooms and one-half above the median. 'Median rooms' is computed on the basis of a standard distribution (see the "Standard Distributions" section under "Derived Measures"). In computing median rooms, the whole number is used as the midpoint of the interval; thus, the category "3 rooms" is treated as an interval ranging from 2.5 to 3.5 rooms. 'Median rooms' is rounded to the nearest tenth. (For more information on medians, see "Derived Measures".)

To calculate aggregate rooms, a value of "10" is assigned to rooms for units falling within the terminal category, "9 or more." (For more information on aggregates, see "Derived Measures".)

Data on rooms have been collected since 1940. In 1970 and 1980, these data were shown only for year-round housing units. Since 1990, these data are shown for all housing units. In Census 2000, this question was asked on a sample basis. In previous decennial censuses, the question on rooms was asked on a 100 percent basis.