A common criticism of repetition research has argued that many of the tests involved have simply measured retention on a short term scale. A study conducted by Karpicke and Bauernschmidt used this principle to determine the major differences between the different types of repetition. The two focused on studying long term retention by testing participants over the course of one week. The participants were either assigned to a uniform schedule or an expanding schedule. No matter what type of spacing was assigned to the ninety-six participants, each completed three repeated tests at the end of their rehearsal intervals. Once those tests were completed, participants came back one week later to complete a final retention test. The researchers concluded that it did not matter what kind of repetition schedule was used. The biggest contribution to effective long term learning was the spacing between the repeated tests (relative spacing).