For all the debate about which Web sites have the best model for reliable reviews — paid or unpaid, anonymous or real name, Angie’s List or Yelp or TripAdvisor — one thing is certain: a robust ecosystem exists online for restaurant and hotel reviews that has changed those industries for the better.

So it is puzzling that there is no such authoritative collection of reviews for physicians, the highest-stakes choice of service provider that most people make.

Sure, various Web sites like HealthGrades and RateMDs have taken their shots, and Yelp and Angie’s List have made a go of it, too. But the listings are often sparse, with few contributors and little of substance.

What we have here is a demand and supply problem: many people want this information, and more consumers would trust it if the sites had more robust offerings. But not enough people take the time to review their doctors. And fixing that problem means figuring out why.

Companies have tried to collect reviews of doctors since the early days of the Web, and RateMDs.com has gathered more than most. The founder, John Swapceinski, was inspired to create it after his success with a site called RateMyProfessors.com, which is well known for the “hotness” rating that college students assign (or not) to their teachers.

“Anything that people spend time or money on ought to be rated,” he said. RateMDs now has reviews of more than 1,370,000 doctors in the United States and Canada.

But getting in the faces of the previously untouchable professional class has inevitably led to legal threats. He says he gets about one each week over negative reviews and receives subpoenas every month or two for information that can help identify reviewers, who believe they are posting anonymously.

Over at Angie’s List, service providers have sued reviewers, whose names are known to the company, “a handful” of times, according to the company. Angie’s List has paid their legal fees in the past, but a co-founder of the site, Angie Hicks, said she could not commit to doing that in every case in the future.

None of the litigants at Angie’s List have been doctors so far, but that doesn’t mean they are thrilled with her health reviews. “They told me that ‘patients aren’t smart enough to figure out whether I’m a good doctor,’ ” she said. “But I told them that these conversations have been happening all along.” The only difference with the site, she pointed out, is that the doctors get to listen in.

Some doctors have silenced patients anyway. Several years ago, a physician reputation management service called Medical Justice developed a sort of liability vaccine. Doctors would ask patients to sign an agreement promising not to post about the doctor online; in exchange, patients would get additional privacy protections.

This struck me as the height of audacity, and when I shared my feelings with the company, I was informed that the agreements had outlived their usefulness. What neither its vice president of marketing, Shane Stadler, nor its founder and chief executive, Jeffrey Segal, told me, however, was that the company had retired the agreements in the wake of a lawsuit related to them and a complaint filed with the Federal Trade Commission.

Medical Justice has now turned 180 degrees and embraced the review sites. It helpfully supplies its client doctors with iPads that they can give to patients as they are leaving. Patients write a review, and Medical Justice makes sure that the comments are posted on a review site.

Sound coercive? Not to Mr. Segal, a lawyer and former neurosurgeon who says he has 150 to 200 active physician accounts for the service. “The reality is that every health care system is asking for feedback, even Medicare,” he said.

Other doctors have taken matters into their own hands. Writing in the online magazine Slate in 2008, Dr. Kent Sepkowitz, of the prestigious Memorial Sloan-Kettering Cancer Center in New York, gleefully recounted his creation of fake reviews on a couple of sites.

These physicians are probably outliers, though. The American Medical Association speaks for most doctors. Robert Mills, a spokesman, sent me a statement that he said was from the A.M.A.’s president, Dr. Peter W. Carmel, that read, in part, “Anonymous online opinions of physicians should be taken with grain of salt and should not be a patient’s sole source of information when looking for a new physician.”

This, however, is almost exactly the same statement it provided to its own publication, American Medical News, in 2008, when it was attributed to Dr. Nancy H. Nielsen, the president-elect of the A.M.A. at the time. Had they achieved some kind of mind meld?

When I pointed this out to Mr. Mills, he got Dr. Carmel to the phone rather quickly.

“To advise people anonymously through an open site when this is an important decision for people’s lives, I don’t think it’s proper,” Dr. Carmel told me. “The evidence that’s given on many of these consumer sites is undocumented, unverified and anonymous. It may well have nothing to do with actual patient treatment.”

Given many physicians’ wariness, it’s understandable that patients may be reluctant to mix it up with them online. But patients may be steering clear for a far more ordinary reason: if they live in a small town or are only one or two degrees of social separation from physicians or their family members, they may not want to create any awkwardness.

An Angie’s List customer who read my column about the service last week raised a related concern. She said she would never talk negatively about her doctors on the site because there were only two decent hospital systems where she lived and she didn’t want to end up blackballed by doctors at either. She wouldn’t let me use her name in this article, given her fear of incurring their wrath.

Others idolize their doctors, which creates its own challenges. Dr. Sam Nussbaum, chief medical officer at the insurance giant WellPoint, which makes patient reviews of its network doctors available for all customers to see, explains it another way. The insurer has found that only roughly 20 percent of customers will switch to a generic drug or use a less expensive imaging center, even if there is no health risk. Why? Because their doctor told them so.

It is exactly this sort of unquestioning mind-set that may cause such low participation (or disproportionately positive reviews) at many review sites. At WellPoint, about 10 percent of the 250,000 doctors in its network have at least one review. The company had planned on posting reviews only after it had at least 10 reviews for a doctor but had to change course. “We wanted statistical validity, but we really had too few doctors listed and wanted to increase that number,” Dr. Nussbaum said.

Perhaps the biggest problem with the ratings is that they are incomplete. WellPoint tracks doctors’ communication skills, availability, office environment and trust, but it doesn’t yet provide information about medical outcomes. While it’s nice to know how long different obstetricians make you wait, it would also be helpful to know how many babies they end up delivering by Caesarean section.

WellPoint knows a lot about a lot of this; in fact it pays many physicians more when they achieve better results. But it’s not ready to share all of its outcome data. “Over time, we’re going to make a lot of changes,” Dr. Nussbaum said. “But the unintended consequences would be if certain surgical specialists would not take on the most challenging, needy and difficult patients.”

Nevertheless, the big health care law requires Medicare to share all sorts of such data about doctors starting Jan. 1, 2013, assuming legal challenges don’t get in the way. The A.M.A. has raised many concerns about “risk adjustments” for the factors Dr. Nussbaum mentioned as well as accuracy, among other things.

Until a single one-stop shop exists for both reviews and data that are fair and useful, we are left with one another. The problem with asking friends for a doctor recommendation is that even if they are a lot like you, they may not have any idea whether the doctor is a good clinician or not.

Careful readers can probably find some sites with listings for certain doctors that in number and detail add up to a useful measure of many of their skills. But you may not know anything about whether the reviewers are people similar to you.

The only solution, then, is to keep populating these sites en masse if you dare and your doctor doesn’t seem to be the suing sort, taking care all the while to tell the truth and be fair. State as much about yourself and your condition as you feel comfortable sharing, and be detailed in your comments and feedback.

No one of us is as smart as all of us, after all. But if most of us decline to contribute to the collected knowledge about the medical community, all of us lose out.