A study published Monday shows that patients often defer to their doctors for fear of being labeled "difficult." But patients who take that approach can hinder their ability to fully participate in decisions about their health, according to the study, which appears in the journal Health Affairs. In the study, 48 Bay Area patients recruited from Palo Alto medical practices said they feared that challenging their physicians or asking too many questions might result in lower-quality care or strain their relationship. But health experts say the rules are changing. The federal health law actually requires shared decision making between patients and doctors as an essential part of its programs.