Premorbid intelligence was assessed using the validated Dutch Adult Reading Test (DART).[27] DART premorbid intelligent scores range from 0 to 100 with higher scores indicating higher levels of premorbid intelligence.
Premorbid intelligence was assessed using the Dutch version of the National Adult Reading Test (NART) [25]; mean estimated IQ for the AD group was 88.1 (S.D. = 13.5) mean estimated IQ for the controls 87.2 (S.D. = 11.4).
Intelligence was assessed using the National Adult Reading Test (Nelson, 1991).
At ages 10 and 12, intelligence was assessed using Internet-based tests.
Non-verbal intelligence was assessed using the Picture Completion Task, a subtest of the "Wechsler Adult Intelligence Scale", revised German version (WAIS-R) [ 35].
Child intelligence was assessed using the composite IQ score on the Kaufman Brief Intelligence Test (K-BIT) (Kaufman et al. 1990) at the time that the CPT was administered.
Verbal intelligence was assessed using the German "Mehrfachwahl-Wortschatz-Test", that is, "Multiple Choice Vocabulary Test" (MWT) [ 33], which resembles the "Spot-the-Word-Test" [ 34].
General intelligence was assessed using the Chinese version of Wechsler Intelligence Scale for Children (WISC-III), which included verbal IQ, performance IQ, and full-scale IQ.
Maternal intelligence was assessed using the Test of Nonverbal Intelligence Third Edition (TONI-3), a language-free measure of general intelligence considered to be relatively free of cultural bias (DeMauro 2001).
A disadvantage of such a combined design is that general intelligence is assessed using different intelligence tests at different points in time, which may affect estimates of the correlation between relatives.
