Playing the odds game without looking into the science and prospects of a company's drug is yet another foolish way to go. Try researching the companies closely before placing a place a short. As an example, Prana has a conservative 20 Billion potential market in it's lead drug candidate, PBT2. Another 1 Billion with the same drug awaiting results for Huntington's. They are taking PBT434 into human trials next year for Parkinson's, a 4 Billion dollar market.
To suggest to anyone to short this stock is really really bad advice. You would be better off just walking away.
The high attrition rate is certainly a fact of biotech investing. For NCE's only about 53% will succeed in Phase II and 36% Phase III. One reason I look for hints of efficacy in Phase IIa data, especially positive comments by the physicians or some hint of accelerated status being requested.