WATCH OUT FOR NUDGES THAT STEER YOU TO TRADE TOO MUCH

ANYONE who has shopped for groceries with a toddler knows to be on high alert for the impulse items the store has thoughtfully placed at a child's eye height.

- KIM CLARK

And these days, grown-ups investing using web platforms or mobile apps must also be on high alert for carefully placed virtual nudges that might encourage impulsive trades. A growing body of research has found that many seemingly innocuous design decisions embedded in investment websites or apps-such as replacing check boxes with swipes or highlighting lists of stocks that have had the biggest price moves-can encourage investors to trade more. That can generate profits for the brokerage, but research has long shown that it can also reduce investors' long-term returns.

Even in an era of zero trading commissions, brokers benefit from trading volume. They might receive a commission for directing your order to a particular market maker, for instance. Or they might simply want to keep you engaged so they can entice you into more-expensive or fee-generating products and services.

Brokerages are in a bind: On the one hand, they want to make their sites as engaging, easy to use and profitable as possible. But they also need to retain their customers' trust.

And regulators are watching as investing moves increasingly online.