A 2020 report by psychologist John Protzko analyzed over 30 studies and found that children have become better at delaying gratification over the previous 50 years, corresponding to an average increase of 0.18 standard deviations per decade on the IQ scale. This is contrary to opinion the majority of the 260 cognitive experts polled (84%), who thought this ability was deteriorating. Researchers test this ability using the Marshmallow Test. Children are offered treats. If they are willing to wait, they get two. If not, they only get one. The ability to delay gratification is associated with positive life outcomes, such as better academic performance, lower rates of substance abuse, and healthier body weights. Possible reasons for improvements in the delaying gratification include higher standards of living, better-educated parents, improved nutrition, higher preschool attendance rates, more test awareness, and environmental or genetic changes. This development does not mean that children from the early twentieth century were worse at delaying gratification and those from late twenty-first will be better at it, however. Moreover, some other cognitive abilities, such as simple reaction time, color acuity, working memory, complexity of vocabulary usage, and three-dimensional visuospatial reasoning have shown signs of secular decline.