[...] Companies were gathering millions of records from pharmacies. They then sold them on to insurers eager to gain a competitive advantage by avoiding people likely to incur high medical fees. Since 1 percent of patients account for over one-fifth of health care costs, and 5 percent account for nearly half of costs, insurers who can “cherry-pick” the healthy and “lemon-drop” the sick will see far more profit than those who take all comers. Prescription data gave insurers the information they needed to tailor policies to exclude preexisting conditions and to impose higher charges for some members.