Mean: The simple arithmetic average for a population; that is, the sum of all the values in a population divided by the size of the population. For this report, population means are estimated by computing the weighted sum of the sample values, then dividing by the sum of the sample weights. The mean is, thus, an aggregate ratio whose denominator is the total number of households or vehicles. See Ratio Estimate.

Measured Heated Area of Residence: The floor area of the housing unit that is enclosed from the weather and heated as collected in the 1993 RECS. Basements are included whether or not they contain finished space. Garages are included if they have a wall in common with the house. Attics that have finished space and attics that have some heated space are included. Crawl spaces are not included even if they are enclosed from the weather. Sheds and other buildings that are not attached to the house are not included. "Measured" area means that the measurement of the dimensions of the home did not rely on the respondent's reports but was an actual measurement by the interviewer using a metallic, retractable, 50-foot tape measure. "Heated area" is that portion of the measured area that is heated during most of the season. Rooms that are shut off during the heating season to save on fuel are not counted. Attached garages that are unheated and unheated areas in the attics and basements are also not counted.

Metropolitan: See Urban.

Metropolitan Statistical Area (MSA): Areas defined by the U.S. Office of Management and Budget in 1992. An MSA is (1) a county or group of contiguous counties that contain at least one city of 50,000 inhabitants or more, or (2) an urbanized area of at least 50,000 inhabitants and a total MSA population of at least 100,000 (75,000 in New England). The contiguous counties are included in an MSA if, according to certain criteria, they are essentially metropolitan in character and are socially and economically integrated with the central city. In New England, MSAs consist of towns and cities, rather than counties. (See Urban, Central City, Suburban, and Rural.)

Metropolitan Status: Refers to the geographic location of the households in relationship to MSA's. See Metropolitan, Nonmetropolitan, and Central City.

Miles per Gallon (mpg): A measure of vehicle fuel economy. Miles per gallon (mpg) as presented in this report represents "fleet miles per gallon." For each subgroup or "table cell," mpg is computed as the ratio of the total number of miles traveled by all vehicles in the subgroup to the total number of gallons consumed. For the 1994 RTECS, mpg values were assigned to each vehicle using the EPA certification files and adjusted for on-road driving.

Mini-Service Pumps: See Type of Primary Service.

Minivan: New type of small van that first appeared with that designation in 1984. Any of the smaller vans built on an automobile-type frame. Earlier models such as the Volkswagen van are now included in this category.

Model Year: As determined by the manufacturer, the model year is the year that appears in the vehicle identification number.

Motor Fuel Consumption: See Vehicle Fuel Consumption.

Motor Fuel Expenditures: See Vehicle Fuel Expenditures.

mpg: See Miles per Gallon.

Miles-per-Gallon (mpg) Shortfall: The difference between actual on-road mpg and EPA laboratory test mpg. Miles-per-gallon (mpg) shortfall is expressed as gallons-per-mile ratio (GPMR).

MSA: See Metropolitan Statistical Area (MSA).

Multistage Area Probability Sample: A sample design executed in stages with geographic "clusters" of sampling units selected at each stage. This procedure reduces survey expense while maintaining national coverage.

Natural Gas: See Main Heating Fuel.

Nonmetropolitan: Households not located within MSAs as defined by the U.S. Office of Management and Budget. See Metropolitan Statistical Area (MSA).

Number of Cylinders: In a reciprocating engine, a cylinder is the chamber in which combustion of fuel occurs and the piston moves, ultimately delivering power to the wheels. Common engine configurations include 4, 6, and 8 cylinders. Generally, the more cylinders a vehicle has, the greater the amount of engine power it has. However, more cylinders often result in less fuel economy. See Engine Size.

Number of Households: The total number of households in the United States that are represented by the sample households. In this report, most statistics are shown for the number of households with vehicles, which is a subset of the total number of households.

Number of Vehicles: See Vehicle and Vehicle Stock.

Occupied Housing Unit: A unit someone was living in as his or her usual or permanent place of residence when the first field contact was made. See Housing Unit.

On-Road Miles per Gallon (mpg): A composite mpg that was adjusted to account for the difference between the test value and the fuel economy actually obtained on the road.

Origin: The primary ethnic background of the person considered to be the householder as self-determined by the respondent. Origin of householder was collected in the 1993 RECS. Each respondent was asked, "Which of the groups on this exhibit best describes the householder?" The groups included: white, black or Negro, American Indian, Alaskan native, Asian, and Pacific Islander. The word "race" was not used in either the questionnaire or the instructions. See Hispanic Descent.

Outside Central City: See Central City.

Passenger Car: See Vehicle and Automobile.

Pickup Truck: Includes compact and full-size pickup trucks. See Vehicle.

Poverty: Low-income classifications to which certain households are assigned based on the household's annual income reported in the 1993 RECS. "Below 100 percent of poverty" encompasses a group of households with incomes below the poverty level as defined by the Bureau of the Census. "Below 125 percent of poverty" includes a group of households with incomes below 125 percent of the poverty level. These groups of the poor and near-poor represent

alternative levels for defining poverty. The definitions of "poor" are based on the number of family members in the household and the income of the entire family.

Premium-Grade Gasoline: A grade of unleaded gasoline with a high octane rating, (approximately 92) designed to minimize preignition or engine "knocking" by slowing combustion rates. See Regular-Grade Gasoline and Intermediate-Grade Gasoline.

Predictive Mean Matching: A model-based procedure used to impute for item nonresponse. This method uses logistic models to compute predicted means that are used to statistically match each nonrespondent to a respondent with the closest predicted mean. The respondent's value is directly imputed to the nonrespondent.

Price: The dollar amount per gallon of fuel purchased. For the 1994 RTECS, fuel prices were not collected directly from the respondent. Instead fuel prices were estimated from the Bureau of Labor Statistics Retail Pump Price Survey and from the Lundberg Survey Inc. Prices

Primary Sampling Unit (PSU): A sampling unit selected at the first stage in multistage area probability sampling. A PSU typically consists of one to several contiguous counties--for example, a metropolitan area with surrounding suburban counties. The approximately 3,100 counties and independent cities of the contiguous United States were grouped into about 1,800 PSUs by a procedure similar to the one used by the Census Bureau for its Current Population Survey. PSUs can be composed of one or more MSAs or can be composed of rural counties.

PSU: See Primary Sampling Unit.

Quadrillion: The number 1,000,000,000,000,000 or 10¹⁵.

Ratio Estimate: The ratio of two population aggregates (totals). For example, "average miles traveled per vehicle" is the ratio of total miles driven by all vehicles, over the total number of vehicles, within any subgroup or "table cell." In this report, there are two types of ratio estimates: those computed using aggregates for vehicles and those computed using aggregates for households. See Mean.

Rear-Wheel Drive: See Type of Drive.

RECS: See Residential Energy Consumption Survey (RECS).

Regression Imputation: A statistical technique for predicting the value of a numerical variable that is missing. The technique involves developing a regression equation that predicts the value of the missing variable based upon variables that are not missing or have already been imputed.

Regular-Grade Gasoline: A grade of unleaded gasoline with a lower octane rating (approximately 87) than other grades. Octane boosters are added to gasoline to control engine preignition or "knocking" by slowing combustion rates. See Intermediate-Grade Gasoline and Premium-Grade Gasoline.

Relative Standard Error: See RSE (Relative Standard Error).

Residential: Occupied housing units, including mobile homes, single-family housing units (attached and detached), and apartments. The definition of "occupied housing units" is the same as that used by the U.S. Bureau of the Census. See Household and Housing Unit.

Residential Energy Consumption Survey (RECS): A national multistage probability sample survey conducted by the Energy End Use Division of the Energy Information Administration. The RECS provides baseline information on how households in the United States use energy. The RTECS sample is a subset of the RECS. Household demographic characteristics reported in the RTECS publication are collected during the RECS personal interview.

RSE (Relative Standard Error): A measure of the reliability or precision of a survey statistic. Variability occurs in survey statistics because the different samples that could be drawn would each produce different values for the survey statistics. The RSE is a measure of precision on a percentage scale. The RSE is defined as the standard error of a survey estimate, divided by the survey estimate and multiplied by 100. (Standard error is the square root of the variance.) For example, an RSE of 50 percent means that the standard error is half as large as the survey estimate.

RSE Column Factor: An adjustment factor that appears above each column of the tables and is used to compute RSEs. For a survey estimate in a particular row and column of a table (that is, a particular "cell"), the approximate RSE is obtained by multiplying the RSE row factor by the RSE column factor for that cell. See RSE and RSE Row Factor.

RSE Row Factor: A factor that appears to the right of each row of the tables, and is used to compute RSE's. For a survey estimate in a particular row and column of a table (that is, a particular "cell"), the approximate RSE is obtained by multiplying the RSE row factor by the RSE column factor for that particular cell. The row factor is equal to the geometric mean of the RSE's in a particular row of the tables. See RSE and RSE Column Factor

Rural: Households not located within Metropolitan Statistical Areas as defined by the U.S. Office of Management

and Budget for 1993. See Metropolitan Statistical Area and Urban Status.

Sampling: The procedure used to select housing units for interview from the population of residential housing units in the United States. See Multistage Area Probability Sample.

Self-Service or Mini-Service: See Type of Primary Service.

Shortfall: See Miles-per-Gallon (mpg) Shortfall.

Sport-Utility Vehicle: Includes light trucks that are similar to jeeps. Other common terms for these vehicles are sport-utility, special purpose, utility or off-the-road vehicles. They may have a four- or two-wheel drive. See Vehicle.

Suburban: Those parts of the MSA that are not designated as central city. Suburban areas are referred to as "outside central city." See Metropolitan Statistical Area.

Transmission Type: The householder was asked if each vehicle had an automatic or manual shift transmission. The transmission is the part of a vehicle that transmits motive force from the engine to the wheels, usually by means of gears for different speeds using either a hydraulic "torque-converter" (automatic) or clutch assembly (manual). On front wheel drive cars, the transmission is often called a "transaxle." Fuel economy is usually higher with manual transmissions than automatic transmissions, although newer automatic transmissions are narrowing the difference.

Transportation Energy Expenditures: See Vehicle Fuel Expenditures and Combined Household Energy Expenditures.

Type of Drive: Refers to which wheels the engine power is delivered to, the so-called "drive wheels." Rear-wheel drive, has drive wheels on the rear of the vehicle. Front-wheel drive, a newer technology, has drive wheels on the front of the vehicle. Four-wheel drive uses all four wheels as drive wheels, and is found mostly on sport-utility vehicles and trucks, though it is becoming increasingly more common on station wagons and vans.

Type of Fuel System: See Carburetor, Fuel-Injection, and Diesel Fuel Systems.

Type of Vehicle Fuel Purchased: The predominant type of fuel purchased during 1994. Data categories are leaded and unleaded gasoline, diesel motor fuel, and "other" which includes propane and gasohol. See Gasoline, Gasohol, Unleaded Gasoline, Leaded Gasoline, Regular-Grade Gasoline, Intermediate-Grade Gasoline, and Premium- Grade Gasoline.

Type of Primary Service: The dominant type of service the respondent uses at the service station. Response categories include "full-service pumps," "self- or mini-service pumps," or "both equally." Mini-service is provided when attendants pump the vehicle fuel but do not provide any other service, such as checking the tire pressure.

Urban: Urban refers to a group of households located within Metropolitan Statistical Areas (MSAs) as defined by the U.S. Office of Management and Budget in 1993. For this report, urban is composed of central city and suburban areas. An MSA is (1) a county or group of contiguous counties that contain at least one city of 50,000 inhabitants or more, or (2) an urbanized area of at least 50,000 inhabitants and a total MSA population of at least 100,000 (75,000 in New England). The contiguous counties are included in an MSA if, according to certain criteria, they are essentially metropolitan in character and are socially and economically integrated with the central city. In New England, MSAs consist of towns and cities rather than counties. (See Central City, Suburban, and Rural.)

Unleaded Gasoline: Contains not more than 0.05 gram of lead per gallon and not more than 0.005 gram of phosphorus per gallon. Premium, regular and intermediate grades are included, depending on the octane rating. See Gasoline, Leaded Gasoline, Regular-Grade Gasoline, Intermediate-Grade Gasoline, and Premium-Grade Gasoline.

Van: Includes large vans. Generally, the distinction between large vans and minivans is made by the respondents' answers to "Type of Vehicle" question. Exceptions were: (1) Volkswagen vans were categorized as minivans, and (2) all other pre-1983 vans were categorized as vans.

Vehicle: For the RTECS, vehicles were any motorized vehicles used by U.S. households for personal transportation. Excluded were: motorcycles, mopeds, large trucks, and buses. Included were: automobiles, station wagons, passenger vans, cargo vans, motor homes, pickup trucks, and sport-utility or similar vehicles. In order to be included, vehicles must be: (1) owned by members of the household; (2) company cars not owned by household members but regularly available to household members for their personal use and are ordinarily kept at home; or (3) rented or leased for 1 month or more. See Vehicle Stock, Vehicles Used on the Job, Automobile, Minivans, Vans, Pickup Trucks, and Sport-Utility Vehicles.

Vehicle Acquisition: The number of vehicles a household acquires or obtains during the RTECS survey year. The average number of vehicles in the stock is computed using these data. See Vehicle Disposition.

Vehicle Disposition: The number of vehicles a household disposes of during the RTECS survey year. Disposed vehicles include those sold, traded, or the owner moved out of the household. The average number of vehicles in the stock is computed using these data. See Vehicle Acquisition.

Vehicle Fuel Consumption: Vehicle fuel consumption is computed as the vehicle-miles traveled divided by the fuel economy reported in miles per gallon (mpg). For the 1994 RTECS, vehicle fuel consumption was derived from the actual vehicle mileage collected in the RTECS and the assigned mpg values were obtained from the EPA certification files and adjusted for on-road driving.

Vehicle Fuel Economy: See Miles per Gallon (mpg).

Vehicle Fuel Expenditures: The cost, including taxes, of the gasoline, gasohol or diesel fuel added to the vehicle's tank. Expenditures do not include the cost of oil or other items that may have been purchased at the same time as the vehicle fuel.

Vehicle Identification Number (VIN): A set of codes, usually alpha-numeric characters, assigned to a vehicle at the factory and inscribed on the vehicle. When decoded, the VIN provides vehicle characteristics. The VIN was used in the 1994 RTECS to help match vehicles to the EPA certification file for calculating miles-per-gallon values. See Environmental Protection Agency (EPA) Certification Files.

Vehicle-Miles Traveled (VMT): The number of miles traveled nationally by the RTECS vehicles for a period of 1 year. In the RTECS, VMT were either calculated using two odometer readings or, for vehicles with less than two odometer readings, imputed using a regression estimate. See Average Vehicle-Miles Traveled.

Vehicle Stock: The number of vehicles owned or used by a household for personal transportation. In the RTECS, with the exception of the statistics reported as of July 1994, a vehicle was defined in terms of a "vehicle year." If a vehicle was present in a household for the entire year, it was counted as one vehicle. If a vehicle was present in a household for one-half of the year, it was counted as only one-half of a vehicle. Therefore, the number of vehicles a sample household was considered as having during the survey year was computed as the days of possession summed over all vehicles in the household, divided by 366 days (1994 was a leap year). See Average Number of Vehicles and Vehicles.

Vehicle Used on the Job: A vehicle used by anyone in the household for job-related activities, excluding commuting to and from work. These vehicles are included in the RTECS. See Vehicle.

VIN: See Vehicle Identification Number.

VMT: See Vehicle-Miles Traveled.

File Last Modified: August 25, 1997