A former market leader that becomes an excellent short sale may in fact show a high price-to-earnings ratio as it's topping and sliding down fast. That may be nice to know, but also know this: Using P-E ratios to select short-sale stock candidates can be hazardous to your portfolio health. Put another way, it's not the high P-E ratio alone that sends a former big winner plunging. The real cause is simply a big shift in the balance between demand