Extractions: Today's Globe Politics Opinion Magazine ... Op-ed March 22, 2005 THERE IS a bumper sticker on the car ahead of me as I drive down Interstate 93. In white letters on a navy background, it proclaims: ''Single-Payer Health Care!'' That's it. There is no argument, no attempt at logic or emotion or humor just an impatient demand for the drastic transformation of one-seventh of the US economy. And note the exclamation point. That is to communicate earnestness, certitude, and indignation classic elements of the liberal approach to policymaking: When promoting radical change, passion and good intentions are what matter most. Real-world consequences count for far less. ADVERTISEMENT As it happens, the real-world consequences of single-payer healthcare also known as socialized medicine or national health insurance are well-documented. Single-payer care exists in Canada, New Zealand, Great Britain, and much of Western Europe. And wherever it has been tried, writes John C. Goodman, president of the National Center for Policy Analysis, ''rationing by waiting is pervasive, putting patients at risk and keeping them in pain.'' In ''Lives at Risk,'' a book published last summer, Goodman and two co-authors, Gerald Musgrave and Devon Herrick, showed that a single-payer system, far from proving a panacea, would make American healthcare much worse than it is. (Some of the book has now been adapted into a monograph for the Cato Institute, ''Health Care in a Free Society.'') The claims endlessly repeated by proponents of socialized medicine that it is more efficient, more equitable, and more affordable than American healthcare are belied by decades of data from countries that have gone the single-payer route.