Under the auspices of the "American Community Survey" (ACS), Multnomah County, Oregon (which includes the city of Portland) was selected as one of four 1996 test sites for the "Continuous Measurement” (CM) option that was being considered for Census 2000 and is now part of the Operation Plan for Census 2010 [12, 14, 17]. There are important conceptual differences between ACS and long form data. As its name suggests, CM, unlike the long form, is not designed to provide a “snapshot” at a single point in time [4, 12, 15]. Instead, it is aimed more at providing information that can monitor change over time. For most users, however, this distinction may not be apparent. It is highly likely that ACS data will be used as if they did represent a snapshot at a given point in time if for no other reason then that ACS is viewed as a replacement for the long form [1,2,3]. Bolstering this viewpoint is the fact that ACS data will have to be “controlled” to independently estimated population and housing values so that its results can be adjusted to provide info rmation on the entire population [15].