incompleteness will remain after these addresses are added to the MAF. In anticipation of that, the Census Bureau will carry out a national block canvass, visiting each census block, and adding any missed housing units to the MAF (while collecting information from global positioning systems for all housing units).

It may be the case that for many well-established blocks in the United States a 100 percent block canvass is wasteful, given that there is little possibility in these blocks of addition or deletion of housing units over time. It would be useful to identify such blocks in advance, since then the block canvass could be restricted to the subset of blocks in need of MAF updating (this is consistent with item C.3 in Appendix A). Given the costs of a 100 percent block canvass, identifying a targeting methodology that does an excellent job of discriminating between those blocks that are very stable over time and those blocks that are likely to have recent additions or deletions (or both) would provide substantial cost savings with possibly only a negligible increase in the number of omissions (or erroneous inclusions) in the MAF. It is likely that administrative records, especially building permit records, commercial geographic information systems, and the ACS could provide useful predictors in discriminating between stable and nonstable blocks. Such targeting is already used in the Canadian census; it uses an address register that is updated intercensally, and field verification is restricted to areas where building permit data indicate the presence of significant new construction (Swain et al., 1992).

To support the determination as to whether any targeting methods might satisfy this need—and, indeed, to facilitate a richer evaluation of MAF accuracy than was possible in 2000—the Census Bureau should ensure that the complete source code history of every MAF address is recoverable. In 2000, the MAF was not structured so that it was possible to fully track the procedural history of addresses—that is, which operations added, deleted, or modified the address at different points of time. Therefore, it was not possible to accurately determine the unique contributions of an operation like LUCA or the block canvass; nor was it possible to assess the degree to which various operations overlapped each other in listing the same addresses. Census Bureau staff ultimately derived an approximate “original source code” for MAF addresses, albeit with great difficulty; see National Research Council (2004b:146-147). Redesign of the MAF database structure was included in the plans to enhance MAF and TIGER during this decade; the Census Bureau should assess whether the new structure will adequately track the steps in construction of the 2010 (and future) MAF.

RECOMMENDATION 4: The Census Bureau should design its Master Address File so that the complete operational history—when list-building operations have added, deleted, modified, or simply replicated a particular address record—can be reconstructed. This information will support a comprehensive evaluation of the Local Update of Census Addresses and address canvassing. In addition, sufficient information should be retained, including relevant information from administrative records and the American Community Survey, to support evaluations of methods for targeting blocks that may not benefit from block canvassing. Finally, efforts should be made to obtain addresses from commercial mailing lists to determine whether they also might be able to reduce the need for block canvassing.