This chart is based on a real study however, the claim that Donald Trump has an IQ of 156 is not. (While some on social media claimed, unsurprisingly, that President Barack Obama was omitted from this list because his IQ score was so low, the real reason is that this data was compiled in 2006, before Obama took office.) Simonton's research was later boiled down into the aforementioned chart for a 2015 article published by US News. By contrast, in the historiometric approach, a person’s IQ is quantitatively estimated based on variables having known correlations with IQ, such as highest level of education, academic honors, scores on college admissions exams, occupation, and preferences. In the conventional approach to measuring IQ, a person is given a standardized test, such as the Wechsler Adult Intelligence Scale, and their score on the test is assumed to reflect their level of intelligence (with some amount of random error). As IQ scores were not available for most of the presidents, Simonton used a historiometric approach to estimate their results: The original chart is based on data from a 2006 study conducted by University of California, Davis psychologist Dean Keith Simonton.