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

5. Definition of Extreme Weights
An important feature of the generalized exponential model (GEM) is the built-in
provision of extreme value (ev) treatment. For this purpose, sampling weights are classified as
extreme (high or low) if they fall outside the interval, median ± 3*interquartile range (IQR), for
some prespecified domains defined usually by design variables corresponding to deep
stratification. 7 The critical values for low and high extreme values will be denoted by b k(l) and
b k(u) , respectively. Within GEM modeling, these critical values were defined as median ±
2.5*IQR, which were conservative when compared with the commonly used standard of median
± 3*IQR. This is because in order to better prevent the adjusted weights from crossing the
standard boundary, weights near but below it (i.e., those that have the most potential to become
extreme) were treated as extreme by GEM as well.
For implementing extreme value control via GEM, the variable m k was defined as the
minimum of b k(u) /w k and one for high extreme weights, and the maximum of b k(l) /w k and one for
low extreme weights, where w k represents the sampling weight before adjustment, and b k(u) and
b k(l) denote the critical values for the extreme weights. (Note that under this definition, for high
extreme weights, the more extreme the weight is, the smaller m k will be, and, conversely, for low
extreme weights, the more extreme the weight is, the bigger m k will be.) Nonextreme weights
had a value of one for m k . The upper and lower bounds for the adjustment factors were defined,
respectively, as the product of m k and the upper and lower boundary parameters of GEM. GEM
allows inputs of up to three different upper and lower boundary parameters (L 1 and U 1 , L 2 and
U 2 , L 3 and U 3 ) for high, non-, and low extreme weights. By applying a small upper boundary
parameter for high extreme weights and a large lower boundary parameter for low extreme
weights, the extreme weights can be controlled in the modeling process.
5.1 Questionnaire Dwelling Unit Extreme Weight Definition
For the questionnaire dwelling unit (QDU)-level weight adjustment, extreme weights
were defined using a nested hierarchy of six domains:
1. State;
2. State sampling region;
3. State by household type;
Levels of household type indicate whether the household has members who are youths,
young adults, or adults, where youth signifies 12 to 17, young adult 18 to 25, and adult 26
or older.
a. Youth, Young Adult, Adult;
b. Youth, Young Adult;
c. Youth, Adult;
d. Young Adult, Adult;
7 Deep stratification refers to the stratification that was used in the sample design. In the case of the 2006
survey, deep stratification refers to the cross-classification of State sampling region by age group.
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