Early Childhood Program Participation, From The National Household Education Surveys Program Of 2012 - U.s. Department Of Education Page 34
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59response rate of 78.7 percent and an overall estimated weighted unit response rate (the product of
the screener weighted unit response rate and the ECPP unit weighted response rate) of 57.8
percent.
The NHES:2012 included a bias analysis to evaluate whether nonresponse at the unit and item
levels impacted the estimates. The term “bias” has a specific technical definition in this context:
it is the expected difference between the estimate from the survey and the actual population
value. For example, if all households were included in the survey (i.e., if a census was conducted
rather than a sample survey), the difference between the estimate from the survey and the actual
population value (which includes persons who did not respond to the survey) would be the bias
due to unit nonresponse. Since NHES is based on a sample, the bias is defined as the expected or
average value of this difference over all possible samples.
Unit nonresponse bias, or the bias due to the failure of some persons or households in the sample
to respond to the survey, can be substantial when two conditions hold. First, the differences
between the characteristics of respondents and nonrespondents must be relatively large. For
example, consider estimating the percentage of preschoolers who can recognize all the letters of
the alphabet. If the percentage is nearly identical for both respondents and nonrespondents, then
the unit nonresponse bias of the estimate will be negligible.
Second, the unit nonresponse rate must be relatively high. If the nonresponse rate is very low
relative to the magnitude of the estimates, then the unit nonresponse bias in the estimates will be
small, even if the differences in the characteristics between respondents and nonrespondents are
relatively large. For example, if the unit nonresponse rate is only 2 percent, then estimates of
totals that comprise 20 or 30 percent of the population will not be greatly affected by
nonresponse, even if the differences in these characteristics between respondents and
nonrespondents are relatively large. If the estimate is for a small domain or subgroup (of about 5
or 10 percent of the population), then even a relatively low overall rate of nonresponse can result
in important biases if the differences between respondents and nonrespondents are large.
Comparisons between the full sample population and the respondent populations were made
before and after the nonresponse weighting adjustments were applied to evaluate the extent to
which the adjustments reduced nonresponse bias. Chapter 10 of the NHES:2012 Data File
User’s Manual contains a detailed description of the nonresponse bias analysis. The NHES
sampling frame variables were used for the unit nonresponse bias analysis for the screener and
topical surveys. The analysis of unit nonresponse bias showed evidence of bias based on the
distributions of the sample characteristics for the survey respondents compared to the full
eligible sample. However, this bias was greatly reduced by the nonresponse weighting
adjustments. In the post-adjusted Screener estimates, the number of estimates showing
measurable and practical differences was reduced approximately in half. The percentage of
estimates with measurable survey and sample differences greater than 1 percentage point was
reduced from 22 to 6 percent for the ECPP survey by the nonresponse weighting adjustments.
When key survey estimates generated with unadjusted and nonresponse adjusted weights were
compared, only a small number of measurable differences were observed. This suggests that
none of these variables were powerful predictors of unit response. Therefore, the unit
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