Bryan Caplan  

There's No Evidence Like No Evidence

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Here's an especially wise observation by David Balan:

So then I asked him whether by "no evidence" he meant that there have been lots of studies directly on this point which came back with the result that more chemo doesn't help, or whether he meant that there was no evidence because there were few or no relevant studies. If the former was true, then it'd be pretty much game over: the case for discontinuing the chemo would be overwhelming. But if the latter was true, then things would be much hazier: in the absence of conclusive evidence one way or the other, one would have to operate in the realm of interpreting imperfect evidence; one would have to make judgments based on anecdotal evidence, by theoretical knowledge of how the body works and how cancer works, or whatever. And good people, maybe I'm being unfair and underestimating this guy, but I swear to you that this fancy oncologist in this very prestigious institution didn't seem to understand the difference between these two types of "no evidence."
And in my experience, most anti-theoretical empirical economists - most notably in labor econ - don't understand the difference either.

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COMMENTS (8 to date)
Ryan writes:

After reading your last sentence the name Jared Bernstein pops right into my head.

Les writes:

I have seen the same clueless response several times from MD's. I suspect that it applies to many or even most MD's.

Dr. T writes:

Surprisingly, general oncology is a specialty where less intellectually capable physicians can thrive. The definitive diagnosis of cancer is made by a pathologist. Surgical treatment, if appropriate, is done by a surgical specialtist. Radiation therapy is overseen by the radiation oncologist. All that's left for the oncologist is chemotherapy, and nearly all cancers have well-defined protocols. The biggest challenge is dealing with the emotional effects of cancer and its treatment, but oncologists refer tough cases to psychiatrists or psychologists.

Thus, I am unsurprised that an oncologist did not understand the "no evidence" problem.

D. M. Sahl writes:

Can't say I'm surprised either. I'm in academics (beh. sci. professor) and my wife is a highly specialized physician (radiologist). It seems about half my friends are professors and half MDs. The MDs are, to a person, exceedingly organized and hard-working. My wife's study marathons during med school were mind boggling. Hand them a 1000-page textbook and they will be able to ace a test on it a week or two later. However, they are not, by and large, intellectual, generally curious people. I find the breadth of their knowledge remarkably narrow. They are wonderful people, but more like top-tier technicians than scholars. One problem with my anecdote here is that all the MDs I know are Hopkins/Mayo/Duke top 5% med student types. Maybe they are a hyper-focused subset temperamentally disinclined to expend time and energy learning about anything other than their specific area.

REL writes:

Yes, I think DM Sahl has a filtering problem. I'm also a radiologist, and the difference is obvious and fundamental to me. It's the difference between "not known to be true" and "known not to be true".

cato writes:

i understand your point, and it is a very good one.

however, only one of those is no evidence, the latter is no evidence.

otherwise you would say "there is evidence that extra chemo has no effect"

but the point still stands. there are two types of thing people mean when they say no evidence. only one is no evidence, the other is evidence of no effect.

Mike Moffatt writes:

Cato is right.

I make a point in the courses I teach to never, ever use the term "no evidence" as it's too misleading. If someone asks a question such as "does X cause Y", I'll give an answer such as:

"There have been a number of studies and all evidence suggests that X does not, in fact, cause Y"


"That's still a fairly open question that needs to be studied more.. we really don't know either way".

The problem is not theorists vs. anti-theorists.. the problem is the appalling misuse of the English language. Given that academic economics puts such an emphasis on math vs. verbal skills, to the point where it is not uncommon to see Econ Profs who can't communicate at all in English, this sloppy use of language should surprise no one.

dearieme writes:

Perhaps this is a little harsh, but I'd reckon anyone who didn't know that distinction as being a little stupid. As in unreflective, lacking analytical capacity, downright dim.

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