efficiency. The specific techniques 

 einployed in the saatple designs constructed 

 for this study include: 



1. Grouping the eligible population 

 into small clusters or sampling 

 units ccanprising an efficient 

 interviewer daily work load. 



2. Grouping the sampling units 

 into city and suburban zones, 

 in each of the three urbanized 

 areas surveyed, to provide 

 approximately proportionate 

 representation. 



3. A further grouping of the 

 sampling units within each 

 zone into geographic or area 

 strata, with an equal number 

 of sampling units in each 

 stratum, to ensure adequate 

 distribution of the sample to 

 all segments of the popvilation 

 of interest. 



k. Using equal probabilities for 

 the selecting of sampling \inits 

 within strata and thereby con- 

 siderably simplifying the formu- 

 las necessary for valid compu- 

 tation of the estimates and of 

 their standard errors. 



A strict probability sample implies 

 the application of completely objective 

 methods for the selection of respondents. 

 In the absence of a list of households or 

 persons eligible for intejrview, the re- 

 quired objectivity is met through the use 

 of area probability sampling techniques. 

 To be satisfied with simple sjrea sampling 

 techniques is not enough, however. Inge- 

 nuity in the use of available resources 

 and facilities can considerably increase 

 the efficiency of one area probability 

 sample over another. 



United States Census Population and 

 Housing data, both published and unpub- 

 lished, are our major resource in the 

 design of efficient probability samples. 

 Unpublished data for small areas, such as 

 enumeration districts vised in collecting 

 census data, may be purchased on special 

 order from the Bureau of the Census. In 

 open country areas maps Indicating the 

 location of dwelling units are available 



32 



from State Highway Ccnmlssions. "Hiis 

 supplementary information may be used for 

 a veuriety of purposes in the design of a 

 sample including stratification, assigning 

 selection probabilities, or for the con- 

 struction of approximately equal-sized 

 sampling units. The sample design outlined 

 below makes use of 1950 census data to 

 establish the areti strata and for the 

 assignment of the sampling units within 

 these strata. Although these data were not 

 used for the direct assignment of selection 

 probabilities, the sampling plan adopted is 

 such that the chance for emy segnent of the 

 aureas surveyed, to be represented in the 

 sample, was approximately proportionate to 

 the nxnnber of occupied dwelling units con- 

 tained within the segment whether it was 

 an enumeration district, census tract, 

 township, urban place, city block, or 

 portion of an enumeration district, etc. 



A sample representative of all house- 

 holds In the urbanized areas of Birmingham, 

 Alabama; Boston, Massachusetts; Detroit, 

 Michigan was selected for this study. In 

 addition, a representative sample of all 

 non-irtilte households located in the rural 

 portion of Orangeburg County, South 

 Carolina was chosen. Bureau of the Census 

 definitions of households, dwelling units, 

 urbanized area, rural territory etc. were 

 employed. Tiie sample designs for the 

 three urbanized areas will be described 

 first. These designs were stratified one- 

 stage sample designs, constructed in 

 accordance with the principles outlined 

 above. Careful control in aLll steps of 

 the sample selection made it possible to 

 know exactly the chance every household 

 cluster or sampling unit had of falling 

 into the sample. 



The first step in the sample design 

 consisted of listing and ordering geo- 

 graphically the census tracts in the 

 central city portions of each of the three 

 urbanized areas. In Detroit, those census 

 tracts with 10 percent or more of the 

 dwelling units occupied by non-white house- 

 holds in 1950 were listed and ordered 

 separately. Similarly, ordered lists of 

 the 1950 Census Enumeration Districts were 

 prepared for those portions of the three 

 urbanized areas which fall outside the 

 central cities. Geographic or area strata 

 were then constructed within the central 

 city zones and the suburban zones for each 



