Hundreds of millions of times a year, people turn to online sites and app-based symptom checkers to help figure out what's ailing them, as well as to see if they should call the doctor — or if it's time for a visit to the emergency room.

But you might as well ask a crystal ball if LeBron is happy in Los Angeles. It's anybody's guess.

At least that's the conclusion of a study published in The Lancet that examines both the promise and reality of symptom checkers.

Researchers looked at a wide range of studies on diagnostic direct-to-consumer digital tools and concluded: “Overall, the current evidence base on direct-to-consumer, interactive diagnostic apps is ... uneven in the information provided and inconclusive with respect to safety and effectiveness.”

While misdiagnosis by human doctors happens about 5 percent of the time, affecting about 12 million U.S. adults annually, according to a 2014 study in BMJ Quality Safety, misdiagnosis by digital symptom checkers happens, on average, about 50 percent of the time.

In another study published in 2015, researchers tested 23 symptom checkers by having them evaluate symptoms derived from 45 clinical vignettes that are used to teach and test medical students. Overall, the symptom checker listed the correct diagnosis first in only 34 percent of cases and put it in the top three diagnoses 51 percent of the time.

Of course, we know you're not going to stop checking out online health info — and you shouldn't. But all symptom-checker digital health sources are not created equal.

The best one (it's ours, we are biased) was developed for the Department of Defense and is available on the Sharecare.com app. (It's a free download.) It has the best questionnaire(s) and data, and is most likely to give correct diagnoses. Plus, it will send you to a nearby doctor (or telemedicine connection) if you want one.

But don't let online results make you think you can determine your own treatment. You know the expression “a lawyer who represents himself has a fool for a client”? Well, a patient who has himself or herself for a doctor is foolish too.

Get your online info, then call your local or telephysician for a consult and/or an appointment.