This post originally discussed a large 2011 study by the Thai Department of Mental Health which suggested that the Thai national IQ was 98. National IQ expert, Jason Malloy, has since thoroughly investigated the issue. Readers are referred to his exhaustive, dissertation length Human Varieties post: HVGIQ: Thailand. Jason determined that the best estimated Thailand IQ was 93.9 and that the median Thailand AQ, based on international tests, was 90.5. But there were a number of caveats — so read the HVGIQ post! Taking into account Richard Lynn’s quality weighting method, as discussed in Intelligence: A Unifying Construct for the Social Sciences, based on these numbers the Final National IQ, which combines IQ and AQ test results, would come out to 92.6. ((93.9 (IQ) x 25 (maximum sample quality for IQ tests) + 90.5 (AQ) x 16 (maximum sample quality for achievement tests*))/(16+25) = 92.6.) For reference, Lynn and Vanhanen (2012) assigned Thailand a Final National IQ of 88.9.
*Lynn and Vanhanen (2012) capped the AQ quality at 16. They assigned two points for each post-2000 PISA and TIMSS study that the given nation participated in. Thailand had participated in all 8 post-2000 studies and was thus given an AQ quality of 16. Since the time of their writing, Thailand participated in TIMSS (2011) and PISA (2012). As more data is now available, the maximum AQ quality should arguably be raised to 20. Raising it from 16 to 20, thus increasing the weight of the Thai AQ scores, would decrease the Thailand Final IQ to 92.4.