Additionally, they investigated the correlation between SAT results, using the revised and recentered form of the test, and scores on the Raven's Advanced Progressive Matrices, a test of fluid intelligence (reasoning), this time using a non-random sample. They found that the correlation of SAT results with scores on the Raven's Advanced Progressive Matrices was .483, they estimated that this correlation would have been about 0.72 were it not for the restriction of ability range in the sample. They also noted that there appeared to be a ceiling effect on the Raven's scores which may have suppressed the correlation. Beaujean and colleagues (2006) have reached similar conclusions to those reached by Frey and Detterman. SAT preparation is a highly lucrative field. The field was pioneered by Stanley Kaplan, whose SAT preparation course began in 1946 as a 64-hour course. Many companies and organizations offer test preparation in the form of books, classes, online courses, and tutoring. The test preparation industry began almost simultaneously with the introduction of university entrance exams in the U.S. and flourished from the start. The College Board maintains that the SAT is essentially uncoachable and research by the College Board and the National Association of College Admission Counseling suggests that tutoring courses result in an average increase of about 20 points on the math section and 10 points on the verbal section. A meta-analysis estimated the effect size to be 0.09 and 0.16 for the verbal and math sections respectively, although there was a large degree of heterogeneity. Montgomery and Lilly (2012) performed a systematic literature review of all published SAT coaching research in search of high quality studies (defined as those with randomized controlled trials). They found that the randomized treatments resulted in V/M gains of +23/32 points for a total of +56; the high quality study that showed the highest score increase was Johnson (1984; San Francisco) which was based on a 30-hour prep course that showed an average increase of 178 points. The Johnson San Francisco study was also the only high quality study found on a prep course of 30 hours or more in length, although validity of this outlier study is uncertain due to the attrition of half the participants. Certain high IQ societies, like Mensa, the Prometheus Society and the Triple Nine Society, use scores from certain years as one of their admission tests. For instance, the Triple Nine Society accepts scores (verbal and math combined) of 1450 or greater on SAT tests taken before April 1995, and scores of at least 1520 on tests taken between April 1995 and February 2005.