December 9, 2014 5:02PM

Debunking the Debunking of Dynamic Scoring and the Laffer Curve

Many statists are worried that Republicans may install new leadership at the Joint Committee on Taxation (JCT) and Congressional Budget Office (CBO).

This is a big issue because these two score-keeping bureaucracies on Capitol Hill tilt to the left and have a lot of power over fiscal policy.

The JCT produces revenue estimates for tax bills, yet all their numbers are based on the naive assumption that tax policy generally has no impact on overall economic performance.

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Meanwhile, CBO produces both estimates for spending bills and also fiscal commentary and analysis, much of it based on the Keynesian assumption that government spending boosts economic growth.

I personally have doubts whether congressional Republicans are smart enough to make wise personnel choices, but I hope I'm wrong.

Matt Yglesias of Vox also seems pessimistic, but for the opposite reason.

He has a column criticizing Republicans for wanting to push their policies by using "magic math" and he specifically seeks to debunk the notion - sometimes referred to as dynamic scoring or the Laffer Curve - that changes in tax policy may lead to changes in economic performance that affect economic performance.

He asks nine questions and then provides his version of the right answers. Let's analyze those answers and see which of his points have merit and which ones fall flat.

But even before we get to his first question, I can't resist pointing out that he calls dynamic scoring "an accounting gimmick from the 1970s" in his introduction. That is somewhat odd since the JCT and CBO were both completely controlled by Democrats at the time and there was zero effort to do anything other than static scoring.

I suppose Yglesias actually means that dynamic scoring first became an issue in the 1970s as Ronald Reagan (along with Jack Kemp and a few other lawmakers) began to argue that lower marginal tax rates would generate some revenue feedback because of improved incentives to work, save, and invest.

Now let's look at his nine questions and see if we can debunk his debunking:

1. The first question is "What is dynamic scoring?" and Yglesias responds to himself by stating it "is the idea that when estimating the budgetary impact of changes in tax policy, you ought to take into account changes to the economy induced by the policy change" and he further states that it "sounds like a reasonable idea."

But then he says the real problem is that conservatives exaggerate and "say that large tax cuts will have a relatively small impact on the deficit—or even that they make the deficit smaller" and that they "cite an idea known as the Laffer Curve to argue that tax cuts increase growth so much that tax revenues actually rise."

He's sort of right. There are definitely examples of conservatives overstating the pro-growth impact of tax cuts, particularly when dealing with proposals—such as expanded child tax credits—that presumably will have no impact on economic performance since there is no change in marginal tax rates on productive behavior.

But notice that he doesn't address the bigger issue, which is whether the current approach (static scoring) is accurate and appropriate even when dealing with major changes in marginal tax rates on work, saving, and investment. That's what so-called supply-side economists care about, yet Yglesias instead prefers to knock down a straw man.

2. The second question is "What is the Laffer Curve?" and Yglesias answer his own question by asserting that the "basic idea of the curve is that sometimes lower tax rates lead to more tax revenue by boosting economic growth." He then goes on to ridicule the notion that tax cuts are self-financing, even citing a column by National Review's Kevin Williamson.

Once again, Yglesias is sort of right. Some Republicans have made silly claims, but he mischaracterizes what Williamson wrote.

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More specifically, he's wrong in asserting that the Laffer Curve is all about whether tax cuts produce more revenue. Instead, the notion of the curve is simply that you can't calculate the revenue impact of changes in tax rates without also measuring the likely change in taxable income. The actual revenue impact of changes in tax rates will then depend on whether you're on the upward-sloping part of the curve or downward-sloping part of the curve.

The real debate is the shape of the curve, not whether a Laffer Curve exists. Indeed, I'm not aware of a single economist, no matter how far to the left (including John Maynard Keynes), who thinks a 100 percent tax rate maximizes revenue. Yet that's the answer from the JCT. Moreover, the Laffer Curve also shows that tax increases can impose very high economic costs even if they do raise revenue, so the value of using such analysis is not driven by whether revenues go up or down.

3. The third question is "So do tax cuts boost economic growth?" and Yglesias responds by stating "the credible research on the matter is very very mixed." But he follows that response by citing research which concluded that "a tax cut financed by reductions in wasteful spending or social assistance for the elderly would boost growth."

But that leaves open the question as to whether the economy does better because of the lower tax burden, the lower spending burden, or some combination of the two effects. But I'll take any of those three answers.

So is he "sort of right" again? Not so fast. Yglesias also cites the Congressional Research Service (which rubs me the wrong way) and a couple of academic economists who concluded that there is "no systematic correlation between the level of taxation and the level of economic growth."

The bottom line is that there's no consensus on the economic impact of taxation (in part because it is difficult to disentangle the impact of taxes from the impact on spending, and that's not even including all the other policies that determine economic performance). But I still think Yglesias is being a bit misleading because there is far more consensus on the economic impact of marginal tax rates and debates about the Laffer Curve and dynamic scoring very often revolve around those types of tax policies.

4. The fourth question is "How does tax scoring work now?" and Yglesias respond to himself by noting that the various score-keeping bureaucracies measure "demand-side effects" and "behavioral effects."

He's right, but CBO uses so-called demand-side effects to justify Keynesian spending, so that's not exactly reassuring news for people who focus more on real-world evidence.

And he's also right that JCT measures changes in behavior (such as smokers buying fewer cigarettes if the tax goes up), and this type of analysis (sometimes called microeconomic dynamic scoring) certainly is a good thing.

But the real controversy is about macroeconomic dynamic scoring, which we'll address below.

5. The fifth question is "Can we take a break from all this macroeconomic modeling?" and is simply an excuse for Yglesias to make a joke, though I can't tell whether he is accusing Reagan supporters of being racists or mocking some leftists for accusing Reagan supporters of being racist.

So I'm not sure how to react, other than to recommend the fourth video at this link if you want some real Reagan humor.

6. The sixth question is "What do current scoring methods leave out?" and Yglesias accurately notes that what "dynamic-scoring proponents want is a model of macroeconomic consequences. They think that a country with lower tax rates will see more investment in physical and human capital, leading to more productivity, and more economic growth."

He even cites my blog post from last month and correctly describes me as believing that it is "self-evidently ridiculous that the current CBO model says higher tax rates would lead to faster economic growth via lower deficits."

I also think he is fair in pointing out that "people sharply disagree about how much tax rates actually influence economic growth" and that "the whole terrain is enormously contested."

But this is why I think my view is the reasonable middle ground. At one extreme you find (at least in theory) some over-enthusiastic Republican types who argue that all tax cuts are self-financing. At the other extreme you find the JCT saying tax policy has no impact on the economy and actually arguing that you maximize tax revenue with 100 percent tax rates. I suspect that Yglesias, if pressed, will agree the JCT approach is nonsensical.

So why not have the JCT—in a fully transparent manner—begin to incorporate macroeconomic analysis?

7. The seventh question is "Has dynamic scoring ever been tried?" and Yglesias self-responds by pointing out that a Treasury Department dynamic analysis of the 2001 and 2003 tax cuts come to the conclusion that "the resulting budget impact would be 7 percent smaller than what was suggested by conventional scoring methods" and "ended with the conclusion that the Bush tax cuts substantially decreased revenue."

In other words, dynamic analysis was not used to imply that tax cuts are self-financing. Indeed, the dynamic score in the example of what would happen if the Bush tax cuts were made permanent turned out to be very modest.

So why, then, are folks on the left so determined to block reforms that, in practice, don't yield dramatic changes in numbers? My own guess, for what it's worth, is that they don't want any admission or acknowledgement that lower tax rates are better for growth than higher tax rates.

8. The eighth question is "Why are we talking about dynamic scoring now?" and Yglesias answers his own question by accurately stating that "the Republican takeover of Congress starting in 2015 gives the GOP an opportunity to either change the scoring rules, change the personnel in charge of the scoring, or both."

He's not just sort of right. He's completely right. I have no disagreements.

9. The ninth question is "Why does the score matter?" and his self-response is "the scores matter because perceptions matter in politics." In other words, politicians don't want to be accused of enacting legislation that is predicted to increase red ink.

Yglesias is also right when he writes that this "effect shouldn't be exaggerated. In the past, Republicans haven't hesitated to vote for tax measures that the CBO says will increase the deficit. That's because they have a strong preference for low tax rates."

At the risk of being boring, I also think he's right about the degree to which scores matter.

The bottom line is that questions #1, #2, #3, and #6 are the ones that matter. Yglesias makes plenty of reasonable points, but I think his argument ultimately falls flat because he spends too much time attacking the all-tax-cuts-pay-for-themselves straw man and not enough time addressing whether it is reasonable for the JCT to use a methodology that assumes taxes have no effect on the overall economy.

But I expect to hear similar arguments, expressed in a more strident fashion, if Republicans take prudent steps—starting with personnel changes—to modernize the JCT and CBO apparatus.

P.S. While tax cuts usually do lead to revenue losses, there is at least one very prominent case of lower tax rates leading to more revenue.

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P.P.S. If the JCT approach is reasonable, why do the overwhelming majority of CPAs disagree? Is it possible that they have more real-world understanding of how taxpayers (particularly upper-income taxpayers) respond when tax rates change?

P.P.P.S. If the JCT approach is reasonable, why do international bureaucracies so often produce analysis showing a Laffer Curve?

There's also some nice evidence from DenmarkCanadaFrance, and the United Kingdom.

December 10, 2013 3:57PM

Progress on the Laffer Curve*

The title of this piece has an asterisk because, unfortunately, we're not talking about progress on the Laffer Curve in the United States.

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Instead, we're discussing today how lawmakers in other nations are beginning to recognize that it's absurdly inaccurate to predict the revenue impact of changes in tax rates without also trying to measure what happens to taxable income (if you want a short tutorial on the Laffer Curve, click here).

But I'm a firm believer that policies in other nations (for better or worse) are a very persuasive form of real-world evidence. Simply stated, if you're trying to convince a politician that a certain policy is worth pursuing, you'll have a much greater chance of success if you can point to tangible examples of how it has been successful.

That's why I cite Hong Kong and Singapore as examples of why free markets and small government are the best recipe for prosperity. It's also why I use nations such as New Zealand, Canada, and Estonia when arguing for a lower burden of government spending.

And it's why I'm quite encouraged that even the squishy Tory-Liberal coalition government in the United Kingdom has begun to acknowledge that the Laffer Curve should be part of the analysis when making major changes in taxation.

UK Laffer Curve

I don't know whether that's because they learned a lesson from the disastrous failure of Gordon Brown's class-warfare tax hike, or whether they feel they should do something good to compensate for bad tax policies they're pursuing in other areas, but I'm not going to quibble when politicians finally begin to move in the right direction.

 

The Wall Street Journal opines that this is a very worthwhile development.

Chancellor of the Exchequer George Osborne has cut Britain's corporate tax rate to 22% from 28% since taking office in 2010, with a further cut to 20% due in 2015. On paper, these tax cuts were predicted to "cost" Her Majesty's Treasury some £7.8 billion a year when fully phased in. But Mr. Osborne asked his department to figure out how much additional revenue would be generated by the higher investment, wages and productivity made possible by leaving that money in private hands.

By the way, I can't resist a bit of nit-picking at this point. The increases in investment, wages, and productivity all occur because the marginal corporate tax rate is reduced, not because more money is in private hands.

I'm all in favor of leaving more money in private hands, but you get more growth when you change relative prices to make productive behavior more rewarding. And this happens when you reduce the tax code's penalty on work compared to leisure and when you lower the tax on saving and investment compared to consumption.

The Wall Street Journal obviously understands this and was simply trying to avoid wordiness, so this is a friendly amendment rather than a criticism.

Anyhow, back to the editorial. The WSJ notes that the lower corporate tax rate in the United Kingdom is expected to lose far less revenue than was predicted by static estimates.

The Treasury's answer in a report this week is that extra growth and changed business behavior will likely recoup 45%-60% of that revenue. The report says that even that amount is almost certainly understated, since Treasury didn't attempt to model the effects of the lower rate on increased foreign investment or other "spillover benefits."

And maybe this more sensible approach eventually will spread to the United States.

...the results are especially notable because the U.K. Treasury gnomes are typically as bound by static-revenue accounting as are the American tax scorers at Congress's Joint Tax Committee. While the British rate cut is sizable, the U.S. has even more room to climb down the Laffer Curve because the top corporate rate is 35%, plus what the states add—9.x% in benighted Illinois, for example. This means the revenue feedback effects from a rate cut would be even more substantial.

The WSJ says America's corporate tax rate should be lowered, and there's no question that should be a priority since the United States now has the least competitive corporate tax system in the developed world (and we rank a lowly 94 out of the world's top 100 nations).

But the logic of the Laffer Curve also explains why we should lower personal tax rates. But it's not just curmudgeonly libertarians who are making this argument.

Writing in London's City AM, Allister Heath points out that even John Maynard Keynes very clearly recognized a Laffer Curve constraint on excessive taxation.


Even Keynes himself accepted this. Like many other economists throughout the ages, he understood and agreed with the principles that underpinned what eventually came to be known as the Laffer curve: that above a certain rate, hiking taxes further can actually lead to a fall in income, and cutting tax rates can actually lead to increased revenues.Writing in 1933, Keynes said that under certain circumstances “taxation may be so high as to defeat its object… given sufficient time to gather the fruits, a reduction of taxation will run a better chance than an increase of balancing the budget. For to take the opposite view today is to resemble a manufacturer who, running at a loss, decides to raise his price, and when his declining sales increase the loss, wrapping himself in the rectitude of plain arithmetic, decides that prudence requires him to raise the price still more—and who, when at last his account is balanced with nought on both sides, is still found righteously declaring that it would have been the act of a gambler to reduce the price when you were already making a loss.”

For what it's worth, Keynes also thought that it would be a mistake to let government get too large, having written that “25 percent [of GDP] as the maximum tolerable proportion of taxation.”

But let's stay on message and re-focus our attention on the Laffer Curve. Amazingly, it appears that even a few of our French friends are coming around on this issue.

Here are some portion of a report from the Paris-based Institute for Research in Economic and Fiscal Issues.

In an interview given to the newspaper Les Echos on November 18th, French Prime Minister Jean -Marc Ayrault finally understood that "the French tax system has become very complex, almost unreadable, and the French often do not understand its logic or are not convinced that what they are paying is fair and that this system is efficient." ...The Government was seriously disappointed when knowing that a shortfall of over 10 billion euros is expected in late 2013 according to calculations by the National Assembly. ...In fact, we have probably reached a threshold where taxation no longer brings in enough money to the Government because taxes weigh too much on production and growth.

This is a point that has also been acknowledged by France's state auditor. And even a member of the traditionally statist European Commission felt compelled to warn that French taxes had reached the point whether they “destroy growth and handicap the creation of jobs”

But don't hold your breath waiting for good reforms in France. I fear the current French government is too ideologically fixated on punishing the rich to make a shift toward more sensible tax policy.

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P.S. The strongest single piece of evidence for the Laffer Curve is what happened to tax collections from the rich in the 1980s. The top tax rate dropped from 70 percent to 28 percent, leading many statists to complain that the wealthy wouldn't pay enough and that the government would be starved of revenue. To put it mildly, they were wildly wrong.

I cite that example, as well as other pieces of evidence, in this video.

P.P.S. And it you want to understand specifically why class-warfare tax policy is so likely to fail, this post explains why it's a fool's game to target upper-income taxpayers since they have considerable control over the timing, level, and composition of their income.

P.P.P.S. Above all else, never forget that the goal should be to maximize growth rather than revenues. That's because we want small government. But even for those that don't want small government, you don't want to be near the revenue-maximizing point of the Laffer Curve since that implies significant economic damage per every dollar collected.

August 30, 2010 7:12AM

The Laffer Curve Strikes Again

In the private sector, no business owner would be dumb enough to assume that higher prices automatically translate into proportionately higher revenues. If McDonald's boosted hamburger prices by 30 percent, for instance, the experts at the company would fully expect that sales would decline. Depending on the magnitude of the drop, total revenue might still climb, but by far less than 30 percent. And it's quite possible that the company would lose revenue. In the public sector, however, there is very little understanding of how the real world works. Here's a Reuters story I saw on Tim Worstall's blog, which reveals that Bulgaria and Romania both are losing revenue after increasing tobacco taxes.

Cash-strapped Bulgaria and Romania hoped taxing cigarettes would be an easy way to raise money but the hikes are driving smokers to a growing black market instead. Criminal gangs and impoverished Roma communities near borders with countries where prices are lower -- Serbia, Macedonia, Moldova and Ukraine -- have taken to smuggling which has wiped out gains from higher excise duties. Bulgaria increased taxes by nearly half this year and stepped up customs controls and police checks at shops and markets. Customs office data, however, shows tax revenues from cigarette sales so far in 2010 have fallen by nearly a third. ...Overall losses from smuggling will probably outweigh tax gains as Bulgaria struggle to fight the growing black market, which has risen to over 30 percent of all cigarette sales and could cost 500 million levs in lost revenues this year, said Bezlov at the Center for the Study of Democracy. While the government expected higher income from taxes in 2010 it has already revised that to the same level as last year. "However, this (too) looks unlikely at present," Bezlov added. Romania, desperately trying to keep a 20 billion-euro International Monetary Fund-led bailout deal on track, has a similar problem after nearly doubling cigarette prices in 2009 then hiking value added tax. Romania's top three cigarette makers -- units of British American Tobacco, Japan Tobacco International and Philip Morris -- contributed roughly 2 billion euros to the budget in taxes in 2009, or just under 2 percent of GDP. They estimate about a third of cigarettes in Romania are smuggled and say this could cost the state over 1 billion euros.

August 22, 2010 2:00PM

Congressional Budget Office Says We Can Maximize Long‐​Run Economic Output with 100 Percent Tax Rates

I hope the title of this post is an exaggeration, but it's certainly a logical conclusion based on what is written in the Congressional Budget Office's updated Economic and Budget Outlook. The Capitol Hill bureaucracy basically has a deficit-über-alles view of fiscal policy. CBO's long-run perspective, as shown by this excerpt, is that deficits reduce output by "crowding out" private capital and that anything that results in lower deficits (or larger surpluses) will improve economic performance -- even if this means big increases in tax rates.

CBO has also examined an alternative fiscal scenario reflecting several changes to current law that are widely expected to occur or that would modify some provisions of law that might be difficult to sustain for a long period. That alternative scenario embodies small differences in outlays relative to those projected under current law but significant differences in revenues: Under that scenario, most of the cuts in individual income taxes enacted in 2001 and 2003 and now scheduled to expire at the end of this year (except the lower rates applying to high-income taxpayers) are extended through 2020; relief from the AMT, which expired after 2009, continues through 2020; and the 2009 estate tax rates and exemption amounts (adjusted for inflation) apply through 2020. ...Under those alternative assumptions, real GDP would be...lower in subsequent years than under CBO’s baseline forecast. ...Under that alternative fiscal scenario, real GDP would fall below the level in CBO’s baseline projections later in the coming decade because the larger budget deficits would reduce or “crowd out” investment in productive capital and result in a smaller capital stock.

There's nothing necessarily wrong with CBO's concern about deficits, but looking at fiscal policy through that prism is akin to deciding who wins a baseball game by looking at what happened during the 6th inning. Yes, government borrowing drains capital from the productive sector of the economy. And nations such as Greece are painful examples of what happens when governments go too far down this path. But taxes also undermine economic performance by reducing incentives to work, save, and invest. And nations such as France are gloomy reminders of what happens when punitive tax rates discourage productive behavior.

What's missing for CBO's analysis is any recognition or understanding that the real problem is excessive government spending. Regardless of whether spending is financed by borrowing or taxes, resources are being diverted from the private sector to government. In other words, government spending is the disease and deficits are basically a symptom of that underlying problem. Indeed, it's worth noting that there's not much evidence that deficits cause economic damage but plenty of evidence that bloated public sectors stunt growth. This video is a good antidote to CBO's myopic focus on budget deficits.

August 18, 2010 3:12PM

What’s the Ideal Point on the Laffer Curve?

There's been a bit of chatter in the blogosphere about a recent post on Ezra Klein's blog, featuring estimates from various economists about the revenue-maximizing tax rate. It won't come as a surprise that people on the right tended to give lower estimates and folks on the left had higher guesses. Donald Luskin of National Review estimated 19 percent, for instance, while Emmanuel Saez, Dean Baker, Bruce Bartlett, and Brad DeLong all gave answers around 70 percent.

There are two things that are worth noting.

First, every single answer is to the right of the Joint Committee on Taxation. The revenue-estimators on Capitol Hill assume that taxes have no impact on overall economic performance. As such, even confiscatory tax rates have very little impact on taxable income. The JCT operates in a totally non-transparent fashion, so it is difficult to know whether they would say the revenue-maximizing tax rate is 90 percent, 95 percent, or 100 percent, but it is remarkable that a mini-bureaucracy with so much power is so far out of the mainstream (it's even more remarkable that Republicans controlled Congress for 12 years, yet never fixed this problem, but that's a separate story).

Second, very few of the respondents made the critically important observation that it should not be the goal of tax policy to maximize revenue. After all, the revenue-maximizing point is where the damage to the overall economy is so great that taxable income falls enough to offset the impact of the higher tax rates. Greg Mankiw of Harvard and Steve Moore of the Wall Street Journal indicated they understood this point since they both explained that the long-run revenue-maximizing rate was lower than the short-run revenue-maximizing rate. But Martin Feldstein of Harvard explicitly addressed this issue and hit the nail on the head.

Why look for the rate that maximizes revenue? As the tax rate rises, the "deadweight loss" (real loss to the economy) rises. So as the rate gets close to maximizing revenue the loss to the economy exceeds the gain in revenue.... I dislike budget deficits as much as anyone else. But would I really want to give up say $1 billion of GDP in order to reduce the deficit by $100 million? No. National income is a goal in itself. That is what drives consumption and our standard of living.

For more information, I think my three-part video series on the Laffer Curve is a good summary of the key issues. I posted them in May 2009, but Cato-at-Liberty has been growing rapidly and many people have not seen them. Part I addresses the theory, and explicitly notes that policy makers should target the growth-maximizing tax rate rather than the revenue-maximizing tax rate. Part II reviews some of the evidence, including analysis of the huge increase in taxable income and tax revenue from upper-income taxpayers following the Reagan tax-rate reductions. Part III looks at the Joint Committee on Taxation's dismal performance.

 

August 1, 2010 7:39AM

With Tax Increases Looming, CBO Does About‐​Face and Frets about Deficits and Debt

Like the swallows returning to Capistrano, the Congressional Budget Office follows a predictable pattern of endorsing policies that result in bigger government. During the debate about the so-called stimulus, for instance, CBO said more spending and higher deficits would be good for the economy. It then followed up that analysis by claiming that the faux stimulus worked even though millions of jobs were lost. Then, during the Obamacare debate, CBO actually claimed that a giant new entitlement program would reduce deficits.

Now that tax increases are the main topic (because of the looming expiration of the 2001 and 2003 tax bills), CBO has done a 180-degree turn and has published a document discussing the negative consequences of too much deficits and debt. A snippet:

[P]ersistent deficits and continually mounting debt would have several negative economic consequences for the United States. Some of those consequences would arise gradually: A growing portion of people’s savings would go to purchase government debt rather than toward investments in productive capital goods such as factories and computers; that “crowding out” of investment would lead to lower output and incomes than would otherwise occur.

...[A] growing level of federal debt would also increase the probability of a sudden fiscal crisis, during which investors would lose confidence in the government’s ability to manage its budget, and the government would thereby lose its ability to borrow at affordable rates. ...If the United States encountered a fiscal crisis, the abrupt rise in interest rates would reflect investors’ fears that the government would renege on the terms of its existing debt or that it would increase the supply of money to finance its activities or pay creditors and thereby boost inflation.

At some point, even Republicans should be smart enough to figure out that this game is rigged. Then again, the GOP controlled Congress for a dozen years and failed to reform either CBO or its counterpart on the revenue side, the Joint Committee on Taxation (which is infamous for its assumption that tax policy has no impact on overall economic performance).

July 21, 2010 2:17PM

The Joint Committee on Taxation’s Voodoo Economics

The Wall Street Journal has an excellent editorial this morning on the obscure -- but critically important -- issue of measuring what happens to tax revenue in response to changes in tax policy. This is sometimes known as the dynamic scoring versus static scoring debate and sometimes referred to as the Laffer Curve controversy.

The key thing to understand is that the Joint Committee on Taxation (which produces revenue estimates) assumes that even big changes in tax policy have zero macroeconomic impact. Adopt a flat tax? The JCT assumes no effect on the economic performance. Double tax rates? The JCT assumes no impact on growth.

The JCT does include a few microeconomic effects into its revenue-estimating models (an increase in gas taxes, for instance, would reduce gasoline consumption), but it is quite likely that they underestimate the impact of high tax rates on incentives to work, save, and invest. We don't know for sure, though, because the JCT refuses to make its methodology public. This raises a rather obvious question: Why is the JCT so afraid of transparency? Here's some of what the WSJ had to say about the issue, including some comparisons of what the JCT predicted and what happened in the real world.

...it's worth reviewing whether Joint Tax estimates are accurate. This is especially important now, because President Obama and Democrats in Congress want to allow the 2003 tax cuts to expire on January 1 for individuals earning more than $200,000. The JCT calculates that increasing the tax rates on capital gains, dividends and personal income will raise nearly $100 billion a year. ...we are not saying that every tax cut "pays for itself." Some tax cuts—such as temporary rebates—have little impact on growth and thus they may lose revenue more or less as Joint Tax predicts. Cuts in marginal rates, on the other hand, have substantial revenue effects, as economic studies have shown. ...So how well did Joint Tax do when it predicted a giant revenue decline from the 2003 investment tax cuts? Not too well. We compared the combined Congressional Budget Office and Joint Tax estimate of revenues after the 2003 tax cuts were enacted with the actual revenues collected from 2003-2007. In each year total federal revenues came in substantially higher than Joint Tax predicted—$434 billion higher than forecast over the five years. ...As for capital gains tax receipts, they nearly tripled from 2003 to 2007, even though the capital gains tax rate fell to 15% from 20%. Yet the behavioral models that Mr. Barthold celebrates predicted that the capital gains cuts would cost the government just under $10 billion from 2003-07 when the actual capital gains revenues over five years were $221 billion higher than JCT and CBO predicted. ...Estimating future federal tax revenues is an inexact science to be sure. Our complaint is that Joint Tax typically overestimates the revenue gains from raising tax rates, while overestimating the revenue losses from tax rate cuts. This leads to a policy bias in favor of higher tax rates, which is precisely what liberal Democrats wanted when they created the Joint Tax Committee.

All of the revenue-estimating issues are explained in greater detail in my three-part video series on the Laffer Curve. Part I looks at the theory. Part II looks at the evidence. Part III, which can be watched below, analyzes the role of the Joint Committee on Taxation and speculates on why the JCT refuses to be transparent.