​NAEP Technical DocumentationSubstitute Schools for the 2024 Eighth-Grade Private School National Science Assessment

Though efforts were made to secure the participation of all schools selected, it was anticipated that not all schools would choose to participate. NAEP uses school substitution to mitigate the effect of bias due to nonresponse. A nonparticipating sampled school is replaced by its substitute when the original school is considered a final refusal.

For the eighth-grade private school science sample, substitute schools were preselected for all sampled schools with known affiliation from the Private School Universe Survey (PSS)-based frame by sorting the school frame file according to the actual order used in sample selection (the implicit stratification). Sampled schools with unknown affiliation were not assigned substitutes.​

Schools were disqualified as potential substitutes if they were already selected in the private school sample or assigned as a substitute for another private school (earlier in the sort ordering).

The two candidates for substitutes were then the two nearest neighbors of the originally sampled school in the frame sort order. To be eligible as a potential substitute, the neighbor needed to be a nonsampled school (for any grade) and within the same explicit sampling stratum (private school affiliation). If both nearest neighbors were eligible to be substitutes, the one with a closer grade enrollment was chosen. If both nearest neighbors had the same grade enrollment (an uncommon occurrence), one of the two was randomly selected.

In the eighth-grade private school science sample, six substitute schools ultimately participated.

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