guinness cited vos savant's performance on two intelligence tests, the stanford-binet and the mega test. she took the 1937 stanford-binet, second revision test at age ten. she claims her first test was in september 1956 and measured her mental age at 22 years and 10 months, yielding a 228 score. this figure was listed in the "guinness book of world records"; it is also listed in her books' biographical sections and was given by her in interviews.