In 1950 some 35 percent of dwellings lacked full indoor plumbing. Many families still did not have telephones or cars. And of course very few people had televisions. A modern American family at the 12th percentile (that is, right at the poverty line) surely has a flushing toilet, a working shower, and a telephone with direct-dial long-distance service; probably has a color television; and may well even have a car. Take into account improvements in the quality of many other products, and it does not seem at all absurd to say that the material standard of living of that poverty-level family in 1996 is as good as or better than that of the median family in 1950.
What do we mean by this? We mean that if you could choose between the two material standards of living, other things being the same, you might well prefer the 12th percentile standard of 1996 to the 50th percentile standard of 1950. But does that mean that most people were poor in 1950? No--because man does not live by bread, cars, televisions, or even plumbing alone.
Imagine that a mad scientist went back to 1950 and offered to transport the median family to the wondrous world of the 1990s, and to place them at, say, the 25th percentile level. The 25th percentile of 1996 is a clear material improvement over the median of 1950. Would they accept his offer? Almost surely not--because in 1950 they were middle class, while in 1996 they would be poor, even if they lived better in material terms. People don't just care about their absolute material level--they care about their level compared with others'.