NAEP uses a focused balanced incomplete block (BIB) or partially balanced incomplete block (pBIB) design to assign blocks or groups of cognitive items to student booklets. Because of the BIB and pBIB booklet designs and the way NAEP assigns booklets to students, NAEP can sample enough students to obtain precise results for each test question while generally consuming an average of about an hour and a half of each student's time.
The "focused" aspect of NAEP's booklet design requires that each student answer questions from only one subject area. The "BIB" or "pBIB" design ensures that students receive different interlocking sections of the assessment forms, enabling NAEP to check for any unusual interactions that may occur between different samples of students and different sets of assessment questions.
In a BIB design, the cognitive blocks are balanced; each cognitive block appears an equal number of times in every possible position. Each cognitive block is also paired with every other cognitive block in a test booklet exactly the same number of times. In a pBIB design, cognitive blocks may not appear an equal number of times in each position, or may not be paired with every other cognitive block an equal number of times. NAEP booklet design varies according to subject area (e.g., geography, mathematics, reading, science, U.S. history, writing).
Once the instrument developer has laid out the configuration of all blocks for each booklet in a booklet map shown here with the following column headings,
|Cognitive block 1||Cognitive block 2||Background question directions||General student background questions||Subject-specific background questions|