Data Dictionary:  Census 1990 
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Survey: Census 1990
Data Source:  Social Explorer; U.S. Census Bureau 
Data set: Social Explorer Dataset (SE)
Table:  T65. Per Capita Income In 1989 Dollars [1] 
Universe: Total Population
Table Details
T65.  Per Capita Income In 1989 Dollars  
Universe: Total Population  

Relevant Documentation:
Excerpt from:  Social Explorer, U.S. Census Bureau; Census of Population and Housing, 1990: Summary Tape File 3 on CDROM [machinereadable data files] / prepared by the Bureau of the Census. Washington: The Bureau [producer and distributor], 1991. 
Summary Tape File 3 > Appendix B. Definitions of Subject Characteristics > Population Characteristics > Income in 1989 > Mean Income 
This is the amount obtained by dividing the total income of a particular statistical universe by the number of units in that universe. Thus, mean household income is obtained by dividing total household income by the total number of households. For the various types of income the means are based on households having those types of income. "Per capita income" is the mean income computed for every man, woman, and child in a particular group. It is derived by dividing the total income of a particular group by the total population in that group.
Care should be exercised in using and interpreting mean income values for small subgroups of the population. Because the mean is influenced strongly by extreme values in the distribution, it is especially susceptible to the effects of sampling variability, misreporting, and processing errors. The median, which is not affected by extreme values, is, therefore, a better measure than the mean when the population base is small. The mean, nevertheless, is shown in some data products for most small subgroups because, when weighted according to the number of cases, the means can be added to obtained summary measures for areas and groups other than those shown in census tabulations.
Care should be exercised in using and interpreting mean income values for small subgroups of the population. Because the mean is influenced strongly by extreme values in the distribution, it is especially susceptible to the effects of sampling variability, misreporting, and processing errors. The median, which is not affected by extreme values, is, therefore, a better measure than the mean when the population base is small. The mean, nevertheless, is shown in some data products for most small subgroups because, when weighted according to the number of cases, the means can be added to obtained summary measures for areas and groups other than those shown in census tabulations.