NEW YORK — Although you can’t control the fact that troubles in China can drag down stocks here by 10 percent in just over a week, you do have control over one crucial factor affecting your portfolio: how much you pay in expenses

It may seem logical to expect the more expensive option to be the better one, but investing isn’t like choosing between fresh and day-old sushi. Low-cost funds historically have performed better than higher-cost rivals, according to Morningstar. That’s because low-cost funds have a built-in advantage: Their higher-cost rivals need to make more just to match their competitors’ performance after expenses are taken into account.

Encouragingly, more investors are choosing lower-cost funds. The latest evidence comes from an August report about how workers are investing in their 401(k) accounts. They paid an average of $54 in fees for every $10,000 invested in stock mutual funds last year, according to the Investment Company Institute. That figure was $74 in 2009 and has been on a steady downward trend for the last decade.

Expenses also dropped in 401(k) plans for bond funds, where keeping expenses low can have an even bigger impact. That’s because bonds are paying slim interest — the 10-year Treasury note has a yield of about 2 percent.

You may not notice when a mutual fund charges its fees. There’s no bill that needs to be paid. Instead, funds simply deduct expenses from their total assets. The total amount deducted, divided by the fund’s total assets, is what the industry calls a fund’s expense ratio.

Some funds charge an additional one-time fee, called a load, to investors when they either enter or exit the fund. Most investors avoid these, and 87 percent of dollars invested in mutual funds in 401(k) accounts last year were in no-load share classes.

Workers who have access to 401(k) accounts generally enjoy lower fund expenses because the plans can grant them access to the “institutional” share classes of funds. These are generally reserved for pension funds and other big investors.