When James Loden, an ophthalmologist, recently peered into a patient's eyes, he was evaluating her for laser surgery to correct her vision. But her eyes were sharp enough to have already scanned Dr. Loden's Nashville, Tenn., office, noting a small water stain on the ceiling in the hallway, the technician's missing name tag, and that exactly 55 minutes elapsed between when she came in the door and when she was seen.

This patient, armed with a quick smile and a hidden tape recorder, was actually a "mystery shopper" from a service paid by Dr. Loden to evaluate his own office. After her appointment, she sat in her car and jotted down notes for her employer, Las Vegas-based Examine Your Practice, which then reported back to Dr. Loden on the experience.

"Perception is reality," says Dr. Loden, who has made a number of changes in his practice based on reports from mystery shoppers. "The patient's perception is all that really matters."

The health-care industry has never been noted for its customer service. But as competition builds amid efforts to encourage patients to comparison-shop for health care, medical facilities and hospitals are increasingly looking for ways to improve the patient experience. Some are turning to mystery-shopping services -- a mainstay of the retail and hotel industries -- which send employees to pose as customers and later report back on how they were treated.

Although health-care mystery shopping made up just 2% of the $600 million in revenue for the mystery-shopping industry in 2004 -- the latest data available from the Mystery Shopping Providers Association -- medical revenues doubled from the prior year. "Before 18 months ago, we hadn't had a single inquiry from health care," says Jeff Hall, president of Ann Arbor, Mich.-based Second to None Inc., a general mystery-shopping company. "We fielded half a dozen in the last year."

Health-care facilities that use mystery shoppers say the reports have led to a number of changes in the patient experience, including improved estimates of wait times, better explanations of medical procedures, extended hours for hospital administration workers, escorts for patients who have gotten lost, and even less-stressful programming on the television in the waiting room.

One big impetus for focusing on patient experience: Beginning Oct. 1, the U.S. Centers for Medicare and Medicaid Services will begin assessing patient satisfaction at hospitals across the country and making that data public. Patients can already compare some measures of clinical care at a Department of Health and Human Services Web site, www.hospitalcompare.hhs.gov. But the new survey will be the first time potential patients can directly compare satisfaction scores across hospitals nationwide.

"No one wants to be at the bottom of the list," says Brad Neet, president of Saint Michael's Hospital in Stevens Point, Wis., who enlisted mystery-shopping patients in his hospital in December 2004. The experience spurred the hospital to improve how it communicates what patients can expect during an exam, and the purpose of tests, says Mr. Neet.

Patient satisfaction is also being incorporated more frequently into hospital executive pay. More than 55% of hospital chief executive officers surveyed last year have "some compensation at risk," based on patient satisfaction, up from only 8% to 10% a dozen years ago, according to Mel Hall, president and CEO of Press Ganey Associates Inc., a South Bend, Ind., company specializing in patient-satisfaction assessment that commissioned the study.

Mystery-shopping services work in a number of ways. Generally, the hospital or doctor's office will know only a range of time during which mystery patients may show up, which can run anywhere from a week to a year. In some cases patients reveal themselves at the end of a visit. Other times the facility may never know who the mystery patients were. Generally, patients pose as uninsured patients, and the fees for health care are paid by the health-care facility.

Mystery patients may make inquiries over the phone, go to a doctor's office or emergency room for a checkup, or in extreme cases, fake symptoms. Barbara Gerber, president of medical mystery-shopping company Devon Hill Associates in La Jolla, Calif., says she once kept hospital staff fooled for 12 hours that she had multiple sclerosis so she could check out a rehabilitation hospital's inpatient unit.

To remember details while remaining undercover, shoppers resort to hiding tape recorders in their bags, jotting details down in appointment books or crosswords, and going to bathrooms to take notes.

Observations can range from the minor to the serious. Courtney Lee once posed as an uninsured patient for 24 hours on an inpatient unit at a Midwestern hospital for Indianapolis-based Perception Strategies mystery-shopping service. When she asked for an additional pillow, she says a nurse said to her, "Why don't you have your husband or friend get you one from the dollar store?"

The hospital was also noisy, according to Ms. Lee, who got a headache from being awakened by staffers walking into her room. "By the time I left, I was exhausted," says Ms. Lee, who was pretending to have the flu.

Medical mystery shopping can raise some thorny issues -- among them the fear that mystery patients will take up time and resources needed by truly sick patients. Mystery-shopping firms say that when shoppers are evaluating emergency rooms, they may be told to visit only during less-busy hours, so they won't make suffering patients wait to see medical staff.

Hospitals and doctor's offices typically tell their staff that mystery shoppers will be showing up (without saying exactly when) and staff and doctors sometimes feel spied on. The medical facilities say that staffers usually do come around and learn to appreciate the value of improving service. And mystery patients also note positive interactions.

OhioHealth, a nonprofit organization of 15 hospitals and other health-care services in Ohio, began rewarding employees who got praise from mystery shoppers with small cash prizes, gift cards, better parking spaces, and public recognition, such as engraving their name on a wall plaque. (The program now includes feedback from other patients and staff, too.) OhioHealth's employee turnover rate dropped to 11.5% in 2006 from nearly 18% in 2000, in part due to the new incentives, says Becky Zuccarelli, system vice president for customer service. OhioHealth spent $44,000 on mystery shopping with Perception Strategies, which covered 240 mystery patient visits over one year. The organization has since established in-house mystery shopping.

When Medical City Dallas Hospital learned from reports by Devon Hill shoppers that patients' level of psychological comfort was low, the hospital developed new scripts for speaking with customers. Now, rather than just asking "Can I get anything for you?" staffers are told to add, "I have the time," according to Britt Berrett, Medical City's CEO and president.

Medical City also simplified terminology and enlarged the font on its signs in response to mystery-shopper complaints. Mr. Berrett says the more than $10,000 the hospital spent on the shopper service was "the best money I ever spent."

Dr. Loden, the Nashville ophthalmologist, responded to his shopper feedback by spending more time with his patients during the initial, free consultation for laser eye surgery and is addressing patient wait times. The percentage of patients who decided after consultation to go through with the surgery rose to over 70% in June and July from 50% in May, which was before he made any changes based on the shopper reports. While it isn't definitive that mystery shopping is the reason for this increase, Dr. Loden says that he is pleased and plans to continue hiring mystery patients on a yearly basis as a checkup.