 This is a 12 week study that will evaluate the efficacy and safety of the 11 mg tofacitinib modified release tablet taken once a day in patients with rheumatoid arthritis who continue taking methotrexate. Results for the modified release tablets will be compared to the efficacy and safety of the 5 mg tofacitinib immediate release tablets taken twice a day in patients with rheumatoid arthritis who continue taking methotrexate. 