Work partners Jon Chintanaroad (left) and Mike Prestano are all smiles now, but founding a tech startup together threatened their friendship — and their business. April Dembosky/KQED hide caption

itoggle caption April Dembosky/KQED

Science-based guidelines say there's no benefit to getting an EKG of heart activity before routine cataract surgery — even if the patient is old. But most doctors order such tests anyway. Bull's Eye/ImageZoo/Corbis hide caption

itoggle caption Bull's Eye/ImageZoo/Corbis

The U.S. Preventive Services Task Force recommends mammograms every other year, while the American Cancer Society endorses annual scans. Kari Lehr/Image Zoo/Corbis hide caption

itoggle caption Kari Lehr/Image Zoo/Corbis

Catharine Becker of Fullerton, Calif., was diagnosed with stage 3 breast cancer at 43 despite having a clean mammogram. The mother of three didn't know she had dense breast tissue until after she was diagnosed. Heidi de Marco/Kaiser Health News hide caption

itoggle caption Heidi de Marco/Kaiser Health News