You should get the OG13 edition -- there some question types that have been phased out or decreased in proportion. Between OG12
-13 approximately 12% of the questions were removed and replaced with newer versions. The changes are subtle but over 2 editions, OG11
will not be representative of the exam so you're better off getting the OG13. In just 1 section for example, there are more "complete the argument" questions and "helps explain". in SC, idioms have gradually been phased out so that international students are not at as much a disadvantage for not knowing some of these idioms.
Verbal and math review books are fine -- at the minimum you should update to OG13 -- there's also the integrated reasoning section that is missing in older sections.
You won't necessarily bomb the exam if you stick with OG11
-- but if you're looking to max your score go for OG13. Read a review of the OG13
for more info.
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