A research study is just a peer-reviewed argument
To make your case in court, you need two things: first, some evidence; and, second, an argument about what the evidence shows.
The same thing is true in sabermetrics, or any other science. You have your data, and your analysis; that's the evidence. Then you have an argument about what it means.
But, most of the time, the "argument" part gets short shrift. Pick up a typical academic paper, and you'll see that most of the pages are devoted to explaining a regression, and listing the results and the coefficients and the corrections and the tests. Then, the author will just make an unstated assumption about what that means in real life, as if the regression has proven the case all by itself.
That's not right. The regression is important, but it's just the gathering of the evidence. You still have to look at that evidence, and explain what you think it means. You have to make an argument. The regression, by itself, is not an argument. The *interpretation* of the regression is the argument.
For instance: suppose you do a simple regression on exercise and lifespan, and you get the result that every extra mile jogged is associated with an increased lifespan of, say, 10 minutes. What does that mean in practical terms? Probably, the researcher will say that if you want Americans' lifespan to increase by a day, we should consider getting each of them to jog 144 more miles than they would otherwise. That would seem reasonable to most of us.
Suppose, now, another study looks at pro sports, and finds that every year spent as a starting MLB shortstop is associated with an extra $2 million in lifetime earnings. Will the researcher now say that if we want everyone to earn an extra $2 million, we should expand MLB so that everyone in the USA can be a starting shortstop? That would be silly.
Still another researcher does a regression to use triples to predict runs scored. That one finds a negative relationship. Should the study conclude that teams stop trying to hit triples, that it's just hurting them? Again, that would be the wrong conclusion.
All three of these regressions have exactly the same structure. The math is the same, the computer software is the same, the testing for heteroskedasticity is the same ... everything about the regressions themselves is the same. The difference is in the *interpretation* of what the regressions mean. The same interpretation, the same argument, makes sense in the first case, but is obviously ludicrous in the other two cases. And even the third case is very different from the second case.
The regression is just data, just evidence. It's the *interpretation* that's crucial, the argument about what that evidence means.
Why, then, do so many academic papers spend pages and pages on the details of the regression, but only a line or two justifying their conclusions? I don't know for sure, but I'd guess it's because regression looks mathematical and scholarly and intellectual and high-status, while arguments sound subjective and imprecise and unscientific and low-status.
Nonetheless, I think the academic world has it backwards. Regressions are easy -- shove some numbers into a computer and see what comes out. Interpretations -- especially correct interpretations -- are the hard part.
If you think my examples are silly because they're too obvious, here's a real-life example that's more subtle: the relationship between salary and wins in baseball, a topic that's been discussed quite a bit over the last few years. If you do a regression on 2009 data, you'll get that
-- the correlation coefficient is .48
-- the r-squared = .23
-- the value of the coefficient is .16 of a win per $1 million spent
-- the coefficient is statistically significant (as compared to the null hypothesis of zero).
That's all evidence. But, evidence of what? So far, it's just numbers. What do they actually *mean*, in terms of actual knowledge about baseball?
To get from the raw numbers to a conclusion, you have to interpret what the regression says. You have to make an argument. You have to use logic and reason.
So you look the coefficient of .16. From that, you can say, in 2009, every extra $6 million spent resulted, on average, in one extra win. I'm happy calling that a "fact" -- it's exactly what the data shows. But, almost anywhere you go from there now becomes interpretation. What does that *mean*, that every extra $6 million resulted in an extra win? What are the practical implications?
For instance, suppose you're a GM and want to gain an extra win next year. How much extra money do you have to spend on free agents? If you want to convince me that you know the answer, you have to take the evidence provided by the regression, and *make an argument* for why you're right.
A naive interpretation might be to just use that $6 million figure, and say, that's it! Spend an extra $6 million, and get an extra win. It seems obvious from the regression, but it would be wrong.
Why is it wrong? It's wrong because there are other causes of winning than spending money on free agents. There's also spending money on "slaves," and spending money on "arbs". Those are much cheaper than free agents. Effectively, some teams get wins almost for free, by having good young players. The teams that don't have that have to spend double, as it were: they have to buy a free agent just to catch up to the team with the cheap guys, and then they have to buy another one to surpass him.
For instance, team A has 80 wins for "free". Team B has 70 wins for "free" and buys another 20 on the free-agent market. The regression doesn't know free from not free. It sees that team B has 10 more wins, but spent an extra $20X dollars, where X is the actual cost of a free agent per win. Therefore, it spits out that it took 2X dollars to buy each extra win, even though it only took X.
That is: the coefficient of dollars per win from the regression is twice what it actually costs to buy one. The coefficient doesn't measure what a naive researcher might think it does.
My numbers are artificial, but I chose numbers that actually come fairly close to real life. Various sabermetric studies have shown that a free agent win actually costs $4.5 million. But regressions for 2008, 2009, and 2010 respectively show figures of $8.9, $6.2, and $12.6 million, respectively -- about twice as much.
Again, the issue is interpretation. If you're just showing the regression results, and saying, "here, figure out what this means," then, fine. But if your paper has a section called "discussion," or "conclusions," that means you're interpreting the results. And that's the part where it's easy to go wrong, and where you have to be careful.
Which brings me, finally, to the point that I'm trying to make: we should stop treating academic studies as objective scientific findings, and start treating them as arguments. Sure, we can remember that academic papers are written by experts, and peer reviewed, and that much of the time, there's no political slant behind them. If we want, we can consider them as generally well-reasoned arguments by experts of presumably above-average judgment.
But they're still arguments.
So when an interesting study is published, and the media report on it, they should treat it as an argument. And we should hold it to the same standards of skepticism to which we hold other arguments. A research paper is like an extended op-ed. The fact that there's math, and a review process, doesn't make them any less argument-like. The New York Times wouldn't present Paul Krugman's column as fact just because he used regressions and peer review, would they?
I googled the phrase "a new study shows." I got 55 million results. "A new study claims" gives only 4 million. "A new study argues" gives only 300,000.
But, really, It should be the other way around. New studies normally don't "show" anything but the regression results. Their conclusions are always "claimed" or "argued".
The word "show" should be used only when the writer wants to indicate that the claim is true, or that it has been widely accepted in the field. At the time his original Baseball Abstract came out, you'd have to say Bill James was "arguing" that the Pythagorean Projection is a good estimator of team wins. But now that we know it's right, we say he "showed" it.
"Show" implies that you accept the conclusion. "Argue" or "claim" implies that you're not making a judgment.
The interesting thing is that the media seem to understand this. Sure, 90 percent of the time, they say "show". But when they don't, it's for a reason. The "claims" and "argues" are saved for controversial or frivolous cases, ones that the reporter doesn't want to imply are true. For instance, "New study claims gun-control laws have no effect on Canadian murder rate." And, "a new study argues that poker is a game of skill, not chance."
It's as if the reporters want to pretend scientific papers are always right, unless they conclude something that the reporter or editor doesn't agree with. But it's not the reporter's job to be implying the correctness of a conclusion, unless the reporter has analyzed the paper, and is writing the article as an opinion piece.
Ninety-nine percent of the time, a research paper does not "show" anything -- it only argues it. Because, correct conclusions don't just pop out of a regression. They only show up when you support that regression with a good, solid argument.