It's all relative.

That couldn't be truer for Vertex Pharmaceuticals' (Nasdaq: VRTX) phase 2 trial combining VX-809 and Kalydeco in cystic fibrosis patients. Earlier this month, the company reported that 46% of patients had a 5-percentage-point improvement in forced expiratory volume in one second, FEV1, a measure of lung function. The biotech also said 30% of patients improved by 10 percentage points.

Turns out, while they were presented as absolute improvements, those numbers were actually relative to placebo, which inflated the numbers because the placebo group's lung function decreased. The number of patients taking the combination that actually improved 5 or 10 percentage points on an absolute basis was 35% and 19%, respectively.

Vertex blamed the issue on a misinterpretation of the data that it received from a contractor responsible for doing the statistical analysis. That's certainly better than being accused of having employees who faked data, like Sequenom (Nasdaq: SQNM), although it still shouldn't happen.

Let's not forget that this was interim data from a trial with a mere 58 patients, 37 of whom got the drug combination. The data was likely to change anyway, something that investors in Celldex Therapeutics (Nasdaq: CLDX) and in companies presenting preliminary data at the American Society of Clinical Oncology annual meeting next week should remember.

Vertex's new data certainly doesn't look as good as it did before, but given how much of a game-changer the combination is for the treatment of cystic fibrosis, whether the drug works is a lot more important than how well it works. If the combination improves lung functions, cystic fibrosis patients will take it because there aren't any other options, besides drugs such as Gilead Sciences' (Nasdaq: GILD) Cayston and Novartis' (NYSE: NVS) Tobi that treat the symptoms of lung infections.

The decrease in placebo group might not be reproducible, but even ignoring that, VX-809 and Kalydeco caused a mean improvement of 4 percentage points in FEV1. If the combination can hit that number in the phase 3 trial, Vertex shouldn't have any problems getting it on the market and quickly reaching blockbuster status.

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