Data Dictionary: ACS 2008 (1-Year Estimates)
you are here: choose a survey survey data set table variable details
Data Source: U.S. Census Bureau
Universe: Workers 16 years and over with earnings
Variable Details
B08121. Median Earnings In The Past 12 Months (In 2008 Inflation-Adjusted Dollars) By Means Of Transportation To Work
Universe: Workers 16 years and over with earnings
B08121003 Median earnings in the past 12 months -- Car, truck, or van - carpooled
Percent base:
None - percentages not computed
Aggregation method:
Median, using bracket table: B08119, interpolation method: Pareto
Relevant Documentation:
Excerpt from: Social Explorer; U.S. Census Bureau; American Community Survey 2008 Summary File: Technical Documentation.
 
Means of Transportation to Work
The data on means of transportation to work were derived from answers to Question 30, which was asked of people who indicated in Question 28 that they worked at some time during the reference week. (See "Reference Week.") Means of transportation to work refers to the principal mode of travel or type of conveyance that the worker usually used to get from home to work during the reference week.

People who used different means of transportation on different days of the week were asked to specify the one they used most often, that is, the greatest number of days. People who used more than one means of transportation to get to work each day were asked to report the one used for the longest distance during the work trip. The category, "Car, truck, or van," includes workers using a car (including company cars but excluding taxicabs), a truck of one-ton capacity or less, or a van. The category, "Public transportation," includes workers who used a bus or trolley bus, streetcar or trolley car, subway or elevated, railroad, or ferryboat, even if each mode is not shown separately in the tabulation. "Carro público" is included in the public transportation category in Puerto Rico. The category, "Other means," includes workers who used a mode of travel that is not identified separately within the data distribution. The category, "Other means," may vary from table to table, depending on the amount of detail shown in a particular distribution.

The means of transportation data for some areas may show workers using modes of public transportation that are not available in those areas (for example, subway or elevated riders in a metropolitan area where there is no subway or elevated service). This result is largely due to people who worked during the reference week at a location that was different from their usual place of work (such as people away from home on business in an area where subway service was available), and people who used more than one means of transportation each day but whose principal means was unavailable where they lived (for example, residents of nonmetropolitan areas who drove to the fringe of a metropolitan area, and took the commuter railroad most of the distance to work).
Limitation of the Data
Beginning in 2006, the group quarters (GQ) population is included in the ACS. Some types of GQ populations have means of transportation distributions that are very different from the household population. The inclusion of the GQ population could therefore have a noticeable impact on the means of transportation to work distribution. This is particularly true for areas with a substantial GQ population.
Question/Concept History
Beginning in 1999, the American Community Survey questions differ from the 1996-1998 questions only in the format of the skip instructions. Beginning in 2004, the category, "Public transportation" was tabulated to exclude workers who used taxicab as their means of transportation.
Excerpt from: Social Explorer; U.S. Census Bureau; American Community Survey 2008 Summary File: Technical Documentation.
 
Median Earnings
The median divides the earnings distribution into two equal parts: one-half of the cases falling below the median and one-half above the median. Median earnings is restricted to individuals 16 years old and over with earnings and is computed on the basis of a standard distribution. (See the "Standard Distributions" section under "Derived Measures.") Median earnings figures are calculated using linear interpolation if the width of the interval containing the estimate is $2,500 or less. If the width of the interval containing the estimate is greater than $2,500, Pareto interpolation is used. (For more information on medians and interpolation, see "Derived Measures.")
Excerpt from: Social Explorer; U.S. Census Bureau; American Community Survey 2008 Summary File: Technical Documentation.
 
Adjusting Income for Inflation
Income components were reported for the 12 months preceding the interview month. Monthly Consumer Price Indices (CPI) factors were used to inflation-adjust these components to a reference calendar year (January through December). For example, a household interviewed in March 2008 reports their income for March 2007 through February 2008. Their income is adjusted to the 2008 reference calendar year by multiplying their reported income by 2008 average annual CPI (January-December 2008) and then dividing by the average CPI for March 2007-February2008.

In order to inflate income amounts from previous years, the dollar values on individual records are inflated to the latest years dollar values by multiplying by a factor equal to the average annual CPI-U-RS factor for the current year, divided by the average annual CPI-U-RS factor for the earlier/earliest year.