The difference isn’t quite that large as many households are just single people and while the female labor force participation rate increased (34% 1945 vs 57% now) the male labor force participation rate declined ( 83% 1948 vs 68% now). https://fred.stlouisfed.org/series/LNS11300001
Similarly there where a great deal of households in the 1940’a with two working adults.
You read that statement incorrectly, the share of dual incomes among married couples doubled.
Married-couple households however have dropped dramatically over time, 76% of households in 1940, 55% of all U.S. households in 1990, and 46% in 2020. “In 1940, married couples with children represented 43 percent of all households; married couples without children represented 33 percent of households”
Sort of interesting, but I think does not negate the point. A dual income household is not necessarily a dual income married couple. For the purpose of calculating dual income households, you have to consider non married romantic partners and even just relatives and roommates. And again, retirees dropping things down.
This effect of the median family being dual income is likely true for now, and false for 1940. It is much stronger if you subset down to "families", but this nuance doesn't likely appear in the "median household income".
That’s not 54.4% as dual income households that’s 54.4% as more than 1 income.
In the 1940’s multi generational households with multiple income earners were common. In 1940 only 7.8% of all households had a single person vs 26.7% by 2010. Working adult children would frequently stay at home until marriage and sometimes past that point.
This is one of those things you need actual data based on similar definitions to compare.
Similarly there where a great deal of households in the 1940’a with two working adults.