An App That Saved 10,000 Lives While most start-ups feverishly track figures like the total number of users, Ron Gutman, the founder and chief executive of the health information start-up, HealthTap, is more interested in a different data point. This week, the start-up heard from its 10,000th user who said the site saved her life. "My local doctor brushed me off and told me it was anxiety without doing any tests at all," wrote one woman who turned to HealthTap after seeing her doctor. After spending two hours on HealthTap, she was told by a doctor who contributes to the site that her condition sounded like a blocked artery. She soon saw a cardiology specialist who later inserted a coronary stent. Since its founding in 2012, the site has logged nearly a billion questions and answers, from simple queries about headaches or the flu, to more complicated ones, like whether mechlorethamine is a cancer medication. Questions are then routed to a physician who is both an expert in that particular field of medicine, and who is determined by an algorithm to be likely to respond fast, Mr. Gutman said. None of that would be possible without the participation of nearly 50,000 doctors who contribute their advice free. Every page on the site has a disclaimer saying that the site "does not provide medical advice, diagnosis or treatment." HealthTap, which is both a Web site and a mobile application, was recognized at its introduction for applying the principles of gaming - features like badges, rewards and reputation scores - to health care. Today, however, that has shifted. If "gamification" was the hot phrase driving new app design 18 months ago, today start-ups are increasingly looking to the principles of behavioral psychology to encourage behaviors and return visits. HealthTap's evolution shows how moving to behavioral psychology has helped it increase its number of users and the number of doctors who offer knowledge on the site at no cost. Instead of the goofy digital awards that were featured in an earlier version of HealthTap, the site's rewards for doctors have been now recast as decorous professional markers of accomplishment. Instead of the "Doogie Howser Award," physicians are given more serious designations like "advocates," "mentors" or "founding experts." A special dashboard on the site provides a slate of ego-boosting statistics and prompts with physicians" reputation scores, user comments and most crucially, areas in which other doctors consider them experts. This way, the site appeals to the value that doctors place on reputation, expertise and authority. It is also marketed to doctors as a way to find new patients. "There's something really powerful in the ability to create positive feedback loops," said Mr. Gutman, who learned through his many conversations with doctors that they craved something simple after days full of appointments - they simply wanted to be thanked. So now, after a person receives an answer from a HealthTap doctor, they are prompted by the system to thank the doctor, or the site, or both. The woman with the blocked artery, for example, was even prompted to indicate if the service saved her life - a smart touch that not only helps the site track its success, but offers incredibly powerful reason for a doctors to keep coming back and answer more questions.