Many companies offer their employees online tools to look up and compare the price of doctor visits and medical treatments, but those tools are underutilized, according to a new study in the American Journal of Managed Care.

The authors of the study, researchers at Harvard Medical School, interviewed 200 members of the California Public Employees Retirement System, which has 200,000 members enrolled in its preferred provider organization for healthcare. Since 2014 system members have been able to go online to research their out-of-pocket expenses for office visits, procedures, imaging and laboratory at various healthcare facilities.

The price-transparency tool displays prices that are specific to the user’s benefits, and provide real-time estimates that account for their deductible and out-of-pocket spending during the year. Members can also use the tool to review their claims history, and some searches displays quality data on each provider, say Harvard researchers.

When the feature was introduced in 2014, California Public Employees Retirement System launched a substantial educational campaign that resulted in 23% of plan members signing up to use it. But of the 200 system members Harvard Researchers interviewed for the study only 17% used the tool frequently and 27% of system members at some point in the past several years.

Use of the online cost comparison tool was low for several reasons, say Harvard researchers. For starters consumers are not used to comparison shopping for healthcare in the same way they might when buying a car or shopping at the grocery store, says lead researcher Hannah Semigran. Other system members didn’t feel comparison shopping helped them because of the limits of their healthcare benefits, she says.

“Several respondents noted that it was unimportant to shop for care because they were already beyond their deductible or because their co-payment for an office visit was always the same,” the survey says. “Many—in particular, those in rural areas—felt it was not useful to shop for care because there was a limited set of providers they could see within their health plan’s provider network. Others were skeptical of the usefulness of the price information on the website because it did not account for the tests or referrals the physician might order during a visit.”

Many system members also used the tool as just one way to find a physician or a particular treatment. “Among those who used the price transparency tool, few made a decision based solely on the tool and instead used it as a supplement to other resources to make provider choices, such as online reviews and referrals from friends and family,” the survey says.