In a 2018 paper, cognitive scientists James R. Flynn and Michael Shayer argued that the observed gains in IQ during the twentieth century—commonly known as the Flynn effect—had either stagnated or reversed, as can be seen from a combination of IQ and Piagetian tests. In the Nordic nations, there was a clear decline in general intelligence starting in the 1990s, an average of 6.85 IQ points if projected over 30 years. In Australia and France, the data remained ambiguous; more research was needed. In the United Kingdom, young children suffered a decline in the ability to perceive weight and heaviness, with heavy losses among top scorers. In the German-speaking countries, young people saw a fall in spatial reasoning ability but an increase in verbal reasoning skills. In the Netherlands, preschoolers and perhaps schoolchildren stagnated (but seniors gained) in cognitive skills. What this means is that people were gradually moving away from abstraction to concrete thought. On the other hand, the United States continued its historic march towards higher IQ, a rate of 0.38 per decade, at least up until 2014. South Korea saw its IQ scores growing at twice the average U.S. rate. The secular decline of cognitive abilities observed in many developed countries might be caused by diminishing marginal returns due to industrialization and to intellectually stimulating environments for preschoolers, the cultural shifts that led to frequent use of electronic devices, the fall in cognitively demanding tasks in the job market in contrast to the twentieth century, and possibly dysgenic fertility.