Even though this year's class of newly public biotechs is showing a stellar performance in the aftermarket, some IPO candidates have been forced to limp out or shelve their plans altogether. This suggests investors continue to evaluate new stories selectively despite the allure of the most robust IPO market in more than five years.

As of last week, 25 of the 33 companies to price an IPO this year were trading at or above their offer price. The group is up a median of 26%. Indeed, 20 companies have outperformed an already strong biotech market, as measured against the performance of the BioCentury 100 index (see "2013 IPO Performance," A3).