MarketWatch Premium: Investors monitor which stocks company insiders sell. They should find out what insiders don’t sell

Should investors pay attention when a higher-up insider sells shares of his company’s stock?

For years researchers’ answer to this question has been “no,” since the insider could have sold for any number of reasons having nothing to do with his opinion about the stock’s prospects — such as buying a house, paying a big tax bill and the like.

This…