Medicare's new comprehensive measure of hospital readmissions shows that at least 20 percent of the hospitals in Illinois, Maryland, Massachusetts, New Jersey, New York and Rhode Island have higher rates of patients returning than the national average. Colorado, Hawaii, Idaho, North Carolina, Oregon, South Carolina, Utah and Washington led the states with the highest proportion of hospitals with low readmission rates. In those states, between 13 and 16 percent of hospitals came in below the national average, the data show. Since 2008, Medicare has been tracking hospital readmission rates and publishing those for three common ailments. In December, the government expanded its disclosure by publishing hospital rates of Medicare patients of all diagnoses who returned within a month for unplanned reasons.