In fact, using their own numbers, it is evident that they have overlooked the most important contributor to the purported household budget crunch -- taxes.Ms. Warren and Ms. Tyagi compare two middle-class families: an average family in the 1970s versus the 2000s (all dollar values are inflation-adjusted). The typical 1970s family is headed by a working father and a stay-at-home mother with two children. The father's income is $38,700, out of which came $5,310 in mortgage payments, $5,140 a year on car expenses, $1,030 on health insurance, and income taxes "which claim 24% of [the father's] income," leaving $17,834, or about $1,500 per month in "discretionary income" for all other expenses, such as food, clothing, utilities and savings.

The typical 2000s family has two working parents and a higher income of $67,800, an increase of 75% over the 1970s family. But their expenses have also risen: The mortgage payment increases to $9,000, the additional car raises the family obligation to $8,000, and more expensive health insurance premiums cost $1,650. A new expense of full-time daycare so the mother can work is estimated at $9,670. Mother's income bumps the family into a higher tax bracket, so that "the government takes 33% of the family's money." In the end, despite the dramatic increase in family income, the family is left with $17,045 in "discretionary income," less than the earlier generation.

The authors present no explanation for why they present only the tax data in their two examples as percentages instead of dollars. Nor do they ever present the actual dollar value for taxes anywhere in the book. So to conduct an "apples to apples" comparison of all expenses, I converted the tax obligations in the example from percentages to actual dollars.

In fact, for the typical 1970s family, paying 24% of its income in taxes works out to be $9,288. And for the 2000s family, paying 33% of its income is $22,374.

Although income only rose 75%, and expenditures for the mortgage, car and health insurance rose by even less than that, the tax bill increased by $13,086 -- a whopping 140% increase. The percentage of family income dedicated to health insurance, mortgage and automobiles actually declined between the two periods.