attempts to contact residents are unsuccessful.
In February 1996 the Census Bureau officially introduced its plan to use sampling for nonresponse follow-up in the 2000 census. That plan calls for a two-stage design. During stage 1, the Census Bureau would conduct follow-up by enumerators in the field to raise the response rate to at least 90 percent of housing units on the MAF in each census tract.6 Once the 90 percent mark has been reached, stage 2 follow-up would be conducted on a 1-in-10 random sample of the remaining housing units. Characteristics for the remaining nonsampled housing units would be estimated on the basis of the random sample. Below, we describe more fully this design and two alternatives that the Census Bureau has considered.
During stage 1 of nonresponse follow-up, the Census Bureau would begin personal visits to nonresponding housing units in the vast majority of tracts, much as in 1990. Field enumerators would visit housing units in the nonresponse follow-up universe, asking residents the questions on the census form or helping them to fill out the form. Residents who were initially mailed the long form would be asked to fill out the long form. Units where no one was contacted on the initial visit would be scheduled for revisits. In contrast to 1990, however, this stage of nonresponse follow-up would cease in a tract once the response rate (initial response plus this work) had reached 90 percent: that is, when a completed census form or confirmation that the dwelling was vacant had been obtained for 90 percent of the addresses to which a census form had been originally mailed. In a tract with a 90 percent or higher initial response rate--which would be rare— no stage 1 nonresponse follow-up would be conducted.
Because the goal of stage 1 nonresponse follow-up is to reach 90 percent as quickly and inexpensively as possible, those responses would not necessarily represent the whole nonresponse follow-up universe. For example, the overall response for a tract could reach 90 percent before any follow-up had occurred in certain blocks. Also, stage 1 responses might tend to exclude housing units with difficult access or where residents were seldom at home.
To allow unbiased estimation for the final 10 percent of housing units in each tract, the Census Bureau's announced plans for stage 2 of nonresponse follow-up include a 1-in-10 random sample of the remaining nonresponding housing units. Consequently, there would be direct enumerations for at least 91 percent of housing units in each tract at the end of stage 2 nonresponse follow-up. In contrast to stage 1, in stage 2 data would be collected for each sampled unit. Enumerators would make repeated visits to a unit-ideally at different times of the day and different days of the week--until a resident
The Census Bureau originally planned to use counties as the geographic unit for controlling completion of stage 1 nonresponse follow-up. That choice drew wide criticism from the Census Bureau's advisory groups and other interested parties: the concern was that many counties are so heterogeneous that a countywide response rate of 90 percent could be achieved while large areas of the county trailed far behind (White and Rust, 1996). In September 1996 the Census Bureau announced a revised plan to reach 90 percent in each tract. Because the country's 65,000 census tracts, which average 4,000 people and 1,500 housing units, are much smaller than the average county, the revised plan will greatly smooth out response rates at the completion of stage 1 nonresponse follow-up.