A study has found that when women in Medicare managed-care plans were asked to contribute a small co-pay, 8 percent of the women decided to forgo mammograms altogether. Insurance plans are increasingly instituting cost-sharing in the form of co-pays with the hope that consumers will consider cost before getting healthcare services. Although the goal is that people will reconsider potentially unnecessary procedures or medicines but not forgo essential services, the study illustrates it does not always work out that way.