Now do inflation adjustment without reference to CPI but to the price of housing.

     Dual-income households were already the most common family structure
     by the 1980s. There hasn’t been an increase in total hours worked by
     married households since Boomers were in their 30s. 

We're a 4-income household because that's the minimum number of typical income earners needed to afford basic bills in a non-major metro market (major metro are more). Given that we don't seem to exist in this economic study, we're probably part of the >1 income household group.

Of note, houses with 4-6+ cars in the driveway (that all leave every day) are common here. The houses aren't especially large.

The author (Cato Institute scholar) presents a super limited view of the economy.

    In 1967, only 5 percent of US families earned
    over $150,000 (inflation adjusted). 

One example is that the $150k club grows in inverse proportion to home affordability.

    In 1960, approximately 68 out of 100 Americans could 
    afford to buy a home. However, by 2019, this number had
    dropped to about 43 out of 100 Americans.

ref: https://www.thezebra.com/resources/home/housing-trends-visua...

ref: https://www.thezebra.com/resources/research/homeownership-st...

ref: https://listwithclever.com/research/home-price-v-income-hist...