Questionnaire Dwelling Unit-Level and Person Pair-Level Sampling ...

Introduction
Appendix C: GEM Modeling Summary for the
Questionnaire Dwelling Unit Weights
This appendix summarizes each questionnaire dwelling unit (QDU) model group
throughout all stages of weight calibration modeling. Unlike much of the other information
presented in this report, this section provides a model-specific overview of weight calibration, as
opposed to a State- or domain-specific one.
For 2006, modeling involved taking four model groups through three adjustment steps:
(1) selected dwelling unit poststratification, (2) respondent dwelling unit nonresponse
adjustment, and (3) respondent dwelling unit poststratification. After the final poststratification,
the adjusted sampling weights were reasonably distributed and did not require the additional
treatment of the extreme value (ev) step.
Model-specific summary statistics are shown in Tables C.1a through C.4b. Included in
these tables, for each stage of modeling, are the number of factor effects included; the high, low,
and nonextreme weight bounds set to provide the upper and lower limits for the generalized
exponential model (GEM) macro; weighted, unweighted, and winsorized weight proportions; the
unequal weighting effect (UWE); and weight distributions. The UWE provides an approximate
partial measure of variance and provides a summary of how much impact a particular stage of
modeling has on the distribution of the new product of weights. For more details on bounds, see
Section 4.1. At each stage in the modeling, these summary statistics were calculated and utilized
to help evaluate the quality of the current weight component under the model chosen.
Occurrences of small sample sizes and exact linear combinations in the realized data led
to situations whereby inclusion of all originally proposed levels of covariates in the model was
not possible. The text and exhibits in Sections C.1 through C.4 summarize the decisions made
with regard to final covariates included in each model. For a list of the proposed initial covariates
considered at each stage of modeling, see Exhibit C.2, and for the list of realized final model
covariates, see Exhibits C.1.1 through C.4.3. The following sections establish a series of
guidelines to assist in their interpretation.
C.1 Final Model Explanatory Variables
For brevity, numeric abbreviations for factor levels are established in Exhibit 3.1
(included here as Exhibit C.1 for easy reference) in Chapter 3. There, a complete list is provided
of all variables and associated levels used at any stage of modeling. Note that not all factors or
levels were present in all stages of modeling, and the initial set of variables was the same across
model groups but may change over stages of modeling. The initial candidates are found in any of
the proposed variables columns for a particular stage of weight adjustment. Exhibits C.1.1
through C.4.3 provide lists of the proposed and realized covariates.
C-3