For directions on reading the variable description see Data Dictionary Introduction.

Availability: 
 

1850	1860	1870	1880	1900	1910	1920	1940	1950	1960	1970	1980	1990
X	X	X	X	X	X	X	X	X	X	X	X	X

Universe: 
All persons. 

Description: 
PERWT indicates how many persons from the whole population each sampled person represents. The samples for 1860, 1870, 1940, 1950, and 1990 are weighted, so PERWT may be used to obtain nationally representative statistics; the use of weights in other years is optional. Alternatively, users may extract an unweighted subset of these samples using the household variable SELFWTHH. See Chapter 2, "Sample Designs." For a further explanation of sample weights see the Chapter 1, "Introduction."

Comparability: 
The weight is identical for all persons within a given household in 1860, 1870, 1940 and 1950, but varies within households in 1990. In other years, PERWT gives the number of persons in the population represented by the sampled person (approximately equal to the sample density). The weights have been adjusted in all years except 1990 to reflect the exact ratio of persons in the population to persons in the sample. See HHWT  for a discussion of this process and the exact weights for each year other than 1860, 1870, 1940, 1950, and 1990. 

Codes: 
See text above.