Selection of the Public-Use-Microdata Samples (1980 PUMS)
A stratified systematic selection procedure with probability proportional to a measure of size was used to select each public-use microdata sample. The sampling elements were the occupied housing unit including all occupants, the person in group quarters or the vacant housing unit. The measure of size was the full sample weight that resulted from the 1980 census ratio estimation procedure described above.
It was also necessary to employ a subsampling scheme to yield microdata samples with a consistent proportion of cases, from area to area, for which place of work, travel time and migration were coded. The subsampling scheme resulted in the occasional designation of selected microdata sample elements for which the place of work, travel time and migration information was blanked. This subsampling scheme was instituted so that the POW/MIG data would be uniformly available for one half of all microdata cases, not half in most areas but more than half in other areas. Thus, each 1-percent microdata sample gives a 0.5-percent sample of records containing POW/MIG data, and the 5-percent microdata sample gives a 2.5-percent sample for POW/MIG data. The subsampling scheme was also based on a probability-proportional-to-size sampling scheme which utilized mmeasures of size based on both the POW/MIG half-sample and full sample weights.
The sample selection procedures were as follows. First, the sample units were stratified during the selection process. This stratification was intended to improve the reliability of the 5-percent, 1-percent, and 0.1-percent samples by defining strata within which there is an appreciable degree of homogeneity among the census sample households with respect to characteristics of major interest.
A total of 102 strata were defined: 72 strata for persons living in occupied housing units; 24 strata for persons in group quarters (GQ); and 6 strata for vacant ousing units.
The sample selection procedures were applied on a state-by-state basis to obtain the microdata samples. Briefly, for any particular state, the procedure to accomplish the sample selection consisted of creating a number of cells in the computer which correspond to each of the strata defined above. A random value was assigned to each cell and the sample edited detail file (i.e., the internal-use microdata from the full census sample) was then passed and the appropriate weight from each sample housing unit/GQ person was cumulated into the cell corresponding to the appropriate stratum for each unit/person. For occupied housing units, the full sample person weight assigned to the householder of the unit was used. For GQ persons, the full sample person weight was used, while for vacant housing units, the full sample housing unit weight was used.
For a given 1-percent sample, when a unit/person caused the cumulation to exceed 100, that unit/person was designated for the sample, and the value of the cell was reset. The procedure was then repeated. For the 5-percent sample selection, the procedure was the same except that the cumulation cut-off was 20 instead of 100. The starting value of each cell was set so as to minimize the likelihood that any one case would be selected into more than one public-use microdata sample, and the overlap among the samples may be considered negligible. There is a small probability that a given individual unit (one with a high census weight) may have been selected into the 5-percent sample more than once, but this duplication should not have any particularly undesirable consequences.
The POW/MIG subsampling operation was performed by first assigning each selected microdata unit, from the POW/MIG coded strata, a measure equal to the ratio of the POW/MIG half-sample weight to the full sample weight for the selected microdata unit. These measures were cumulated from the selected microdata sample units until the cumulation exceeded 2. The POW/MIG data for the units which caused the cumulation to exceed 2 was retained; otherwise, the POW/MIG information was blanked.
Source: Census of Population and Housing, 1980: Public-Use Microdata Samples Technical Documentation / prepared by the Data User Services Division, Bureau of the Census. Washington: The Bureau, 1983.
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