Need help with flaw question

[swifty]

A 30 year old patient is diagnosed with pancreatitus.  Pancreatitus is usually
caused by one of two factors, excessive alcohol use or gall stones
blocking the pancreatic tract.  Gall stone usually do not develop
until the age of 35 (age, race, or sex are not a factor).  The patient stated he had been drinking excessively for three months and tests found elevated liver enzymes.  More tests found gall stones,  but were inconclusive as to whether the stones were blocking the pancreatic tract. Therefore, the pancreatitus was most likely caused by excessice alcohol use.

Describe the flaw, if any, from the authors conclusion. 

[dsong02]

if there is a flaw, it seems like he is assuming something he is trying to prove.

he diagnoses someone with pancreatitus without knowing for sure what caused it...

[EnglishToLaw]

I see two potentially flaws in the reasoning, but, as we all know, that's probably one too many for the LSAT test writers. For starters, it's noted that pancreatitus is "usually" caused by the alcohol use or the gall stones blocking the tract, so there could be other reasons. Also, the tests were "inconclusive" about whether the stones were blocking the tract; that does not mean they WEREN'T blocking the tract, but that the tests couldn't say one way or the other. So concluding that the pacreatitis is "most likely caused by excessive alcohol abuse" seems shaky on both grounds. What were the answer choices given?

[jacy85]

The most obvious flaw is that the author is that there are two choices, A and B, and either one can cause C.  A is present, and B is present.  The author is relying on the fact that since there's no conclusive proof that A is the cause, then B must be the cause.

Whenever they rely on lack of evidence as the proof that something else is the cause, there's your flaw.  Lack of conclusive evidence is NEVER proof.

[cnkis]

Just because the results with the gall stones is inconclusive, it doesn't mean that it is conclusively the excessive drinking. Meaning that the gall stones could still be the cause and being inconclusive isn't enough to completely rule them out.
  There are a lot of questions like that, where it's two options and since you can't prove one, it's DEFINITELY the other. The answer usually goes: it presumes without justification that drinking is the only cause of the health problems or something to that sentiment. Hope this helps.