I think I'm reasonably knowledgeable about shorting, and not only have I never heard of "on special" but I don't think the concept as you've described it makes any sense. First of all, shorts don't pay interest to borrow stocks, rather, the brokerage firm splits the interest on the short account (the money that results from selling the stock). The short either get no interest on the short account (if they're small) or some fraction (50-80%) of interest the brokers would get (if they have a large, active account). If a stock is hard to borrow, then usually the broker has to pay the firm loaning the stock a higher % of the interest and will thus reduce the amount they pay a short.
I have never heard - ever - of a broker firm paying *extra* interest for "easy to borrow" stocks.
You are somewhat correct in stating that you can make it more difficult for shorts if you remove stocks from your margin account. This is because only stocks in margin accounts can be loaned out, and if enough people do it, sometimes a short squeeze can be organised. Notice this has nothing to do with the interest rate, but rather the stock is called and people are forced for buy it back.
Radisys has 1.34M shares short as of middle of April, out of 7.9M shares total - a fairly high number. The number went down from March to April. The shorts had nothing to do the recent price decline - it was longs selling out and shorts buying.
I've noticed the same refrain on quite a few message boards from non-professional investors, who seem to blame "shorts" and "market markers" for all of the price swings in a stock. Sometime there's just more sellers than buyers...
Mike |