Essentials of Stanford-Binet Intelligence Scales (SB5) assessment, by Gale H. Roid and R. Andrew Barram, says on p. 59, "The two routing subtests in Item Book 1-- Object Series/Matrices and Vocabulary-- can be combined to form an estimated IQ, called the Abbreviated Battery IQ (ABIQ)." It goes on to say that the basis of the estimate is the combination of fluid reasoning (matrices) with crystallized knowledge (vocabulary).
In "
Use of the SB5 in the Assessment of High Abilities", Deborah Ruf cautions against the use of the ABIQ in assessing high-ability children ("Although the ABIQ does provide a good screening indicator of general ability and correlates highly with FSIQ, it nevertheless incorporates only two subtests. A low (or high) score on one of the subtests may give a very different impression of overall ability than would be the case if more diverse subtests were included in the assessment").
It looks like your son did very well on the matrices subtest, shown in his Fluid Reasoning score of 150. If his vocabulary subtest score was 139ish or a little higher, it explains why the ABIQ is 148.
I guess the reason is just that once they have a cutoff and decide what that is, it makes sense to just use the most complete information available. They already let a child qualify on full scale, verbal, or nonverbal IQ above the cutoff number. I guess the ABIQ is just too abbreviated for their taste.
I wonder if the problem is that vocabulary is highly trainable, plus half of the ABIQ number, making it more of a achievement-type metric. I don't know.
