Ariad Pharmaceuticals Inc fka ARIA

[glass_half_full]

If I had to take a guess (which is to say, I don't know the answer for certain) I think it would have to do with how broadly the market's poor performance is affecting issues outside the narrow indexes, S&P500 and DJ Comp.

However, this could cut either of two ways:

If the short interest holders have concentrated long positions in big names, then you would expect Ariad to outperform when the S&P has a bad day (causing margin calls) but other off-index stocks do better. The comparison with the Russel would suggest this isn't the case.

If the shorts are concentrated in, for example, other biotechs or other small- to mid-caps that aren't on the S&P, then the effect would be strongest when the market downdraft is broadest, with many sectors showing weakness.

</speculation>