A value of 100 means that a family with the median income has exactly enough income to qualify for a mortgage on a median-priced home.
The annual income required to buy the median-priced home here, according to experts, is about $50,000.
It found that 57 percent of American families - 56 million of them - could not afford a median-priced home in the area where they live.
This was still 5.5 percent higher than a median-priced home sold for a year ago.
But the typical family in the Northeast had only 93.5 percent of the purchasing power needed to buy a median-priced home there.
Taxes on a median-priced home of about $170,000 are about $7,140 a year.
In greater New York, for instance, only 22 percent of households can buy a median-priced home.
That means that a family earning $43,373 had 94.8 percent of the income needed to qualify to buy the median-priced home at $136,700.
This is especially prominent in California, where only 16% of the population could afford the median-priced home during 2005.
During the last quarter of 1991, it took an income of $52,066 to qualify for a mortgage on a median-priced home.