Is our federal tax system fair? Unfair? Two new studies reach opposite conclusions, findings that may be relevant as Congress and voters debate several pending bills.

On April 15, the Boston Globe, citing a recent study by two professors, Thomas Piketty of the Paris School of Economics and Emmanuel Saez of the University of California, Berkeley, wrote, “The tax burden in the U.S. is shifting away from the rich, to the point where in a few years it could change from being progressive to effectively flat, a new study says.” In tax talk, “flat” means one rate applies to all taxed income.

But two days earlier, Investors Business Daily, citing a study by economists Andrew Chamberlain and Gerald Prante of the Tax Foundation, reported that the tax code was both progressive and fair, with the most productive people paying most of the taxes and receiving the least spending in return. This paper took account not only of taxes paid but also benefits to the public from government spending, a more comprehensive approach to appraising “fairness.”

In both cases, “progressive and fair” signifies that those with more income pay a higher share of that income in taxes. Which study is right, or at least more persuasive?

Messrs. Piketty and Saez, whose study appears in the current Journal of Economic Perspectives, examined four federal taxes — individual, corporate, estate, and payroll — over the past 40 years. Whereas average tax rates for the middle class have hardly changed, they have plunged for the very rich. The top 0.1% of earners paid about 60% of their income in federal taxes in 1970, while they paid only about 40% of their income in 2000.

But, looking at a different measure, the fraction of total taxes paid, Messrs. Piketty and Saez concluded that the share of total taxes paid by the top 0.1% has increased from about 6% to 11% of the total over the same period. That suggests increased progressivity, some argue. But the authors believe that what is important for the progressivity of the system is not the share of total taxes paid, but the percent of a person’s income paid in taxes.

There’s a big problem with comparisons from the pre-1988 period to the present. The Tax Reform Act of 1986, by eliminating some deductions, played havoc with measures of income and hence income distribution. Declines in the top individual marginal rate to 28% from 50% and the top corporate rate to 34% from 46% took full effect in 1988.

It then became advantageous for small businesses to file returns as individuals, rather than as corporations, because the individual tax rate was lower, and approximately 90% of them do so, according to the Small Business & Entrepreneurship Council. Hence, income that was previously reported and taxed as corporate flowed into individual returns, giving the impression that income was increasing.

This makes a difference. Looking at the period between 1988 and 2000, the percent of income paid in federal taxes by the top 0.1% was unchanged at 40%, whereas the share of taxes paid rose to 11% from 7%. By this measure, taxes became more progressive.

Messrs. Chamberlain and Prante took an entirely different approach. Rather than focusing solely on federal individual taxes, they analyzed the distribution of all taxes paid — federal, state, and local. They looked at fifths of the population and didn’t produce data for fractions of the top percent. They analyzed the period between 1991 and 2004, thereby avoiding the pitfalls of comparing incomes before and after 1988.

And they added another dimension to the analysis. They analyzed government spending and which income groups it benefits — all government spending for goods and services, and also transfer payments to individuals, such as unemployment benefits and Social Security.

Households in the two lowest quintiles — a quintile is one-fifth of the whole — received 51% of all government spending because they received more transfer payments. Messrs. Chamberlain and Prante concluded that “both taxes and spending appear to have large distributional effects on households,” and that our tax system is very progressive. The share of total taxes paid by the top quintile rose to 49% in 2004 from 46% in 1991, after peaking at 51% in 2000.

Households in the lowest fifth of incomes received about $8 in federal, state, and local spending for every tax dollar they paid, whereas households in the top fifth of earners received only 41 cents. This shows a tax system with substantial progressiveness.

Looking at the burden of taxes paid in light of benefits received makes far more sense than looking at these taxes in isolation, so Messrs. Chamberlain and Prante are more persuasive.

This question of fiscal fairness — taxes and spending — is more important than settling an arcane dispute among academic economists. The perception of the unfairness of our economic system, as exemplified by our tax code, is prompting a wide range of congressional bills that go far beyond the tax increases scheduled to occur in 2010 unless Congress acts.

These bills all have a common theme — expanding the social safety net to protect the so-called “have-nots” from the “haves.” Proposals include requiring employers to pay a higher minimum wage, a bill which passed in the Senate but has yet to emerge from the House; to give workers a designated number of days of paid sick leave; to upgrade 13 weeks of unpaid maternity leave to paid leave, and even to set guidelines for wages paid to male- and female-dominated occupations.

Despite their negative effects on hiring, there may be reasons to pass some of these bills. But the unfairness of our tax system is not one of them.

Ms. Furchtgott-Roth, former chief economist at the U.S. Department of Labor, is a senior fellow at the Hudson Institute.