Table 1.
Classification accuracy of Unidimensional and Bi-factor approaches for 10 advanced placement tests.
| Test | Year | Disattenuated Correlationa | NIbCR | NIcMC | Sample size | Accuracy by Unidimensional (%) | Accuracy by Bi-factor (%) | Accuracy improvement |
|---|---|---|---|---|---|---|---|---|
| English Literature | 2010 | 0.778 | 3 | 55 | 20,000 | 60.90 | 65.56 | 4.65% |
| English Literature | 2009 | 0.77 | 3 | 55 | 20,000 | 63.04 | 67.17 | 4.13% |
| English Language | 2009 | 0.81 | 3 | 55 | 20,000 | 63.62 | 67.56 | 3.94% |
| English Language | 2010 | 0.807 | 3 | 54 | 20,000 | 63.37 | 67.15 | 3.78% |
| European History | 2009 | 0.92 | 7 | 80 | 20,000 | 68.77 | 70.33 | 1.56% |
| World History | 2009 | 0.89 | 3 | 70 | 20,000 | 69.70 | 70.75 | 1.05% |
| US History | 2010 | 0.908 | 3 | 80 | 6936d | 69.32 | 70.24 | 0.92% |
| European History | 2008 | 0.89 | 7 | 80 | 20,000 | 68.14 | 69.06 | 0.92% |
| World History | 2008 | 0.91 | 3 | 70 | 20,000 | 70.92 | 70.07 | 0.85% |
| Physics B | 2008 | 0.96 | 7 | 70 | 11,941 | 76.73 | 77.06 | 0.33% |
a
The disattenuated correlation denotes the estimated true score correlation between the subtest scores for the MC and CR items; they were provided by College Board.
b
The number of CR items included in the tests.
c
The number of MC items included in the tests. To maximize the comparability of results, we used 3 CR items and 55 MC items for all 10 tests.
d
US History 2010 data set had a sample size of 20,000. However, only 6936 students chose the same three CR items (i.e., #1, #3, and #4 items).