Tuesday, July 10, 2012

Partisan Statistic Alert

Some people are touting the statistics reported here, which show that the national debt has increased by a smaller percentage under Obama than the four previous presidents.
Reagan - 189% Bush - 55% Clinton - 37% Bush - 86% Obama - 35%
I double-checked the numbers, and they are technically correct. But they’re also meaningless.

First, these figures compare presidents instead of presidential terms. It shouldn’t be surprising that a two-term president will tend to rack up more debt than a one-term president.

Second, this is one of those instances where percentages are completely misleading. Each administration inherits the debt built up by all previous administrations, and that inherited debt provides the denominator for calculating the percentage increase. As a result, the percentage is automatically pulled downward for later presidents simply because they are later.

(For comparison, imagine if the entire $14.9 trillion in debt accumulated since 1980 had been added in equal-sized chunks by all eight presidential terms. That would be $1.87 trillion per term. Yet the percentages wouldn’t be equal at all. They would decline in every single year, from a high of 201% for Reagan 1 to a low of 13% for Obama.)

So what happens when we correct for both errors? Correcting the term problem first, and also adjusting dollars for inflation (something else I don’t think the original source did), here are the percentage increases by presidential term:


Now Obama’s record isn’t the best. He has the third highest percentage increase, and he hasn’t even finished his term yet. (I used the most recent national debt figures, which you can find here. For pre-1993 figures, see here.)

But again, the percentage is misleading. It would be better to look at the absolute dollar increase (again, adjusted for inflation). Here’s what you get:


Now it becomes clear: Compared to the previous seven presidential terms, Obama has presided over the largest increase in the national debt. And again, his term isn’t over yet.

Obviously, Obama’s defenders will say his actions were justified. He inherited a terrible economy, a large stimulus was necessary to boost performance, some expenditure increases were outside Obama’s control, etc. Those arguments might even be right, and they’re free to make them… but only after admitting that the national debt did, in fact, increase dramatically during Obama’s term.

One final addendum: these numbers could, of course, be adjusted in many other ways as well. You could adjust for the size of GDP or population. You could change the start-and-end dates to reflect who passed the relevant budgets, or to reflect that a presidential term doesn’t start until about a month after the election; doing so would shift some of Obama’s debt into Bush II’s second term (as well as shorten Obama’s effective time in office). In truth, there’s something inherently silly about trying to attribute changes in the national debt to specific presidents at all, since additional debt results from a complex interplay of policies created by multiple presidents and congresses over time. All I’m really trying to correct here is two very obvious errors that the creators of these particular statistics should have seen instantly, and probably would have seen if they didn’t have partisan blinders on.

13 comments:

Ran said...

> Second, this is one of those instances where percentages are completely misleading.

I think that's a matter of opinion. What would it mean if every president were equally fiscally irresponsible? You take that to mean that each president increases the debt by a constant real amount, such that the debt increases linearly (after adjusting for inflation). "Some people" apparently take that to mean that each president increases the debt by a constant nominal proportion, such that the debt increases exponentially (without adjusting for inflation). (Given that other important statistics — interest, population, GDP, etc. — increase exponentially, "some people" don't seem so unreasonable to me. I'm not saying they're right, but it's also not obvious to me that they're wrong.)

Probably the best comparison for a given purpose will depend on that purpose. And when the purpose is "outright politicking", the best comparison will necessarily involve a lot of cherrypicking. :-P

Glen Whitman said...

Ran, I'm not assuming that the debt should increase linearly. I gave that as just an example, to show that even when the increase is linear, the percentage decreases.

More importantly, using the percentage increase creates a bias in favor of presidents who happen to come into office facing a larger debt. Suppose, for instance, that President A creates a massive increase in the debt relative to whatever responsible standard you choose (linear, exponential, whatever). Then President B inherits a larger debt, which means that any amount that he adds to the debt will look smaller in percentage terms. If we go with your exponential rate of increase, either (a) the higher run-up of debt by President A gives President B the license to spend more, because his "allowed percentage increase" will correspond to more dollars; or (b) the higher run-up of debt by President A will cause any "return to responsibility" by President B to look exceptionally low in percentage terms.

However, as I said in the original post, there is a reasonable argument for adjusting for population or GDP, and you raise a good point about interest. It might be better to use the national debt minus interest.

Ran said...

> Ran, I'm not assuming that the debt should increase linearly.

I understand that; but you're assuming that, in a simplified model, the debt will increase linearly if each president is equally fiscally irresponsible. That is, you're assuming that absolute increase is the appropriate measure, and unless I'm misunderstanding you, your only argument against the proportional-increase measure is that it gives different results from your assumed-appropriate measure. (In technical terms: I think you're "begging the question".)

Let me assume, for the sake of argument, the opposite position: that proportional-increase is the appropriate measure. I can easily reflect your entire comment back at you, especially the second paragraph:

> More importantly, using the absolute increase creates a bias against presidents who happen to come into office facing a larger debt. Suppose, for instance, that President A creates a massive increase in the debt relative to whatever responsible standard you choose (linear, exponential, whatever). Then President B inherits a larger debt, which means that any amount that he adds to the debt will look bigger in absolute terms. If we go with your linear rate of increase, either (a) the higher run-up of debt by President A forces President B to spend less, because his "allowed absolute increase" will correspond to a lower percentage; or (b) the higher run-up of debt by President A will cause any "return to responsibility" by President B to look exceptionally low in absolute terms.

Ran said...

(A tweak: my sentence "Then President B inherits a larger debt, which means that any amount that he adds to the debt will look bigger in absolute terms" should probably be something like "Then President B inherits a larger debt, which means that any percentage that he adds to the debt will look bigger in absolute terms", since "amount" tends to imply absolute terms.)

Glen Whitman said...

Ran, the short answer is YES, I do think absolute change is the right measure. And I don't think this is ideological.

I agree that it might make sense to adjust for GDP or population and interest. (I'm too lazy to do the calculations right now, but feel free.) But once you've adjusted for those factors, I can't think of any justification for setting a baseline of proportional growth instead of absolute growth. Even if you're a progressive liberal who wants to increase the size of the state, it doesn't follow that you'd want to do it via debt instead of taxes.

And furthermore, even if you do accept a normative baseline of proportional growth, looking at percentage change is the wrong way to get at it. Percentage change always measures the president's performance relative to the accumulated debt from previous presidents -- which obviously differs from president to president, and therefore means you're not comparing apples to apples. If you really do believe in proportional growth as the correct baseline, you still have to account for some presidents deviating from your chosen baseline and thus throwing off your measurement of subsequent presidents.

Here's a simple example. Suppose President A leaves the country with $1 of debt, when it previously had $0. President B adds another dollar, leaving the country with $2 debt. President C runs wild, blowing money on booze and hookers, and leaving the country with $102 debt. President D only blows money on booze (no hookers) and leaves the country with $153 debt. Their respective percentage increases are: A - infinity, B - 100%, C - 5000%, and D - 50%. Does it make any sense to rank president D as the best because he has the lowest percentage increase? Or would it be more reasonable to say D looks good only because he followed C? And does it make sense to say A is the worst because he has an infinite percentage increase? Or would it make more sense to say he looks bad only because the previous president left the country with zero debt?

Ran said...

Your example could just as well read: President C runs wild, establishing programs that spend money on booze and hookers. President D really reins in spending, killing the hooker programs and establishing no new expenditures. Looked at this way, sure — President D did a great job attacking the debt problem. There's no "spin-free" way to perform the comparison: a variety of approaches make sense. I think — and IIUC, you largely agree with me on this — that the main problem is with the very attempt to reduce the comparison to a univariate bar-chart, as though a single figure could meaningfully capture a president's effect on the debt.

And President A's infinity-percent is academically interesting, but it's far outside reality. Remember, we're looking to compare real presidents' debt increases. Complaining that the comparison breaks down at the extremes is like refusing to use Newtonian physics on the grounds that it doesn't account for quantum mechanics and relativity. (Though to be honest, even for President A, I think a case could be made that the proportional-increase is meaningful: I think most people would agree that a $1 increase in debt is almost "a drop in the bucket" when the debt is already $153, but is a much bigger deal when the starting-point is no debt at all. The value of a dollar is nonlinear. However, the proportional-increase clearly isn't the whole picture: I think most people would also agree that even when the starting-point is no debt at all, there's a big difference between creating a $1 debt and creating a $1000 debt!)

DKR said...

Forget names of Presidents, the American people own the debt. After all, not one President or member of Congress elected themselves and in many cases elected them over and over again. I'm continually amazed by the stats that show Congress with a dismal approval rating yet the turnover at each election doesn't reflect that same level of disapproval. So, one has to conclude that a majority of Americans think it's someone other than their Congressman or President that is the problem. We better get very critical of the people we elect and get self-honest. Debt is debt no matter who does it or under what excuse is used to do it. I've helped vote out two straight Representatives in my district, one Republican and one Democrat and will do my best to do so again because they just don't get it.
P.S. Would you folks in Pelosi's district please either vote her out or finish the lobotomy she obviously began at some point and didn't get finished.

Philip Whitman said...

I agree with you that this is one of those instances where percentages are completely misleading. However, I don't necessarily agree with you that "It shouldn’t be surprising that a two-term president will tend to rack up more debt than a one-term president." Look at Bill Clinton. He served two terms, yet the debt increased a relatively small amount in his first term and actually decreased during his second term.

Glen Whitman said...

That's why I said a two-termer will "tend to" rack up more debt. Clinton is the exception. In general, the debt has increased during almost every presidential term. And regardless, you need to compare terms instead of presidents in order to make an apples-to-apples comparison.

Philip Whitman said...

Would you agree with me that the fairest thing would be to publish the raw absolute data, and let people decide for themselves what the data mean. They could calculate any percentage they want and decide what it means.

Arne Langsetmo said...

"Second, this is one of those instances where percentages are completely misleading. Each administration inherits the debt built up by all previous administrations, and that inherited debt provides the denominator for calculating the percentage increase. As a result, the percentage is automatically pulled downward for later presidents simply because they are later."

But each president has to pay off (at least interest on) the accumulated debt of the previous administrations as well.

Glen Whitman said...

"Would you agree with me that the fairest thing would be to publish the raw absolute data, and let people decide for themselves what the data mean. They could calculate any percentage they want and decide what it means."

That's the case now. The numbers are publicly available, and people can crunch them however they want. My point was that the way they've been crunched by certain interested parties doesn't make much sense.

Glen Whitman said...

Arne -- that is a good point. Sometimes the national debt figures are published net of interest expense, and those might be better figures to use. Of the two data sources I used, only one of them provides interest expense numbers. I'd be curious to see how the results might change based on better data. My suspicion is that it won't make a huge difference, because interest expense is a fairly small fraction of the national debt as a whole -- and it's the size of the debt as a whole that drives the bias I'm talking about. But I could be wrong.