One element not accounted for by the two noninterview factors above is the systematic differences that exist between characteristics of households that return census mail forms and those that do not (Weidman et al., 1995). The same element has been observed in the ACS across response modes. Virtually all noninterviews occur among the CAPI sample, and people in these HUs may have characteristics that are more similar to CAPI respondents than to mail and CATI respondents. Since the noninterview factors (
NIF1 and
NIF2 ) are applied to all HUs interviewed by any mode, compensation may be needed for possible mode-related noninterview bias. The mode bias factor ensures that the total weights in the cells defined by a cross-classification of selected characteristics are the same as if the weight of noninterview HUs had been assigned only to CAPI HUs, but the factor distributes the weight across all respondents (within the cells) to reduce the effect on the variance of the resulting estimates.
The first step in the calculation of the mode bias noninterview factor (
MBF ) is to calculate an intermediate factor, referred to as the mode noninterview factor (
NIFM ). The
NIFM is not used directly to compute an adjusted weight; instead, it is used as a factor applied to the
WVMS weight to allow the calculation of the
MBF . The cross-classification cells are defined for building type by tabulation month. Only HUs interviewed by CAPI and noninterviews are placed in the cells. If a cell contains fewer than 10 interviewed HUs, it is collapsed with an adjoining month. Cells with no noninterviews are never collapsed unless they are forced to collapse with a neighboring cell that fails the size criterion. The
NIFM for a cell is:
This mode noninterview factor is assigned to all CAPI-interviewed occupied and temporarily occupied HUs. HUs for which interviews are completed by mail or CATI, vacant HUs, and deleted HUs are given a factor of 1.0. Noninterviews are given a factor of 0.0. The
NIFM factor is used in the next step only. Note that the
NIFM adjustment is applied to the
WVMS weight rather than the HU weight after the first and second noninterview adjustments (
WNIF1 and
WNIF2 ). The computation of the weight after the mode noninterview adjustment factor is summarized in Table 11.8.
Table 11.8
Computation of the Weight After the Mode Noninterview Adjustment Factor ( WNIFM )
Interview status |
WNIFMij
|
Occupied or temporarily occupied HU |
WVMS 1 ij × NIFMi
|
Vacant or deleted HU |
WVMSij
|
Noninterviewed HU |
0 |
where
WNIFMij = Adjusted HU weight after the mode noninterview adjustment for the
j th HU within the
i th adjustment cell.
Next, a cross-classification table is defined for tenure (three categories: HU owned, rented, or temporarily occupied), tabulation month (12 categories), and marital status of the householder (three categories: married/widowed, single, or unit is temporarily occupied). All occupied and temporarily occupied interviewed HUs are placed in their cells. If a cell has fewer than 10 interviewed HUs, the cells with the same tenure and month are collapsed across all marital statuses. If there are still fewer than 10 interviewed HUs, the cells with the same tenure are collapsed across all months. The mode bias factor (
MBF ) for each cell is then calculated as:
All interviewed occupied and temporarily occupied HUs are adjusted by this mode bias factor, and the remaining HUs receive the factor 1.0. These adjustments are applied to the
WNIF2 weights. The computation of the weight after the mode bias factor is summarized in Table 11.9 below.
Table 11.9
Computation of the Weight After the Mode Bias Factor ( WMBF )
Interview status |
WMBFij
|
Occupied or temporarily occupied HU |
WNIF 2ij x MBFi
|
Vacant, deleted or noninterviewed HU |
WNIF 2ij |
where
WMBFij = Adjusted HU weight after the mode bias factor adjustment for the
j th HU within the
i th adjustment cell.