The Marshmallow Test Results Have Improved Over Time

Children, on average, are significantly better at delaying gratification in the "marshmallow test" than they were 50 years ago. The abstract of the new paper is as follows:

Have children gotten worse at their ability to delay gratification? We analyze the past 50 years of data on the Marshmallow test of delay of gratification. Children must wait to get two preferred treats; if they cannot wait, they only get one. Duration for how long children can delay has been associated with a host of positive life outcomes. Here we provide the first evidence on whether children’s ability to delay gratification has truly been decreasing, as theories of technology or a culture of instant gratification have predicted. Before analyzing the data, we polled 260 experts in cognitive development, 84% of who believed kids these days are getting worse or are no different. Contrary to this prediction, kids these days are better able to delay gratification than they were in the past, corresponding to a fifth of a standard deviation increase in ability per decade. 

The magnitude of the change is comparable to that of the Flynn effect that was observed in the same time period, i.e. a secular increase in average IQ over time. As the introduction in the body text of the paper explains:

All cognitive abilities have undergone secular increases over the past century (Flynn, 1984). The increase generally runs between 2.3–3 points of overall intelligence per decade (around 1/5 of a standard deviation; Trahan et al., 2014).

The reason for this not known and this empirical result contradicts conventional wisdom in the field.

Some examinations of the Flynn effect have pointed to the improvements mostly coming from a reduction in the number of people scoring at the low end of IQ tests, rather than an improvement at the top, suggesting that a decline in developmental disabilities, perhaps due to better pre-natal care and reduced pollution (e.g. from lead exposure) or improved nutrition, could be a factor, which might also apply to the Marshmallow test improvements over time, even if the Marshmallow test implicates cognitive abilities orthogonal to IQ that involve different brain processes.

Notably, another mention of the related concept of "attention" has remained constant over time in a study comparing results in 1983 to those in 2012, despite increasing diagnosis of attention deficit disorder conditions.

UPDATE: The Marshmallow Test study may be seriously flawed. The truth may actually be  that  Marshmallow Test results are unchanged. Eliminating three very earlier outliers from 1968-1971 from the meta-analysis shows an unvarying trend line from 1971 to the present. The strong implication is that methodological flaws in the first few tests were not recognized and caused the time that children were willing to wait to be much shorter than in all subsequent replications of the study.

Thus, rather than supporting a Flynn effect for patience, it actually confirms the result that attention tests are unchanged in the similar time period which makes sense because the traits related to attention and the Marshmallow Test appear to be closely related (and also related to the Big Five personality trait "conscientiousness" and the trait known as "grit").