The USA showed a 5% increase to 15% between 1940 and 1980 followed by a period of stabilization until 2020. Sweden also had the same increase from about 7% to below 15% over the same period. This country then experiences a downfall and a fast growth to 20% in 2020. On the other hand, Japan witnessed no changes throughout the period from 1940 to 2000 even though there was a slight decrease to below 5% between 1960 and 1980. In the year of 2020, Japan rose to nearly 10%, which doubles the proportion in 2000.
In the year 2040, all three countries are predicted to have a nonstop rise to 25% or higher, and Japan