5 hours, 1 day, 5 days, 25 days, 4 months, and 2 years. criticism spaced repetition with expanding intervals has long been argued to be the most beneficial version of this learning procedure, but current research, which compared repetition procedures, has shown the difference between expanding repetition and uniform retrieval is either very little to nonexistent. some researchers have found cases where uniform retrieval is better than expanding. the main speculation for this range of results is that prior research has not accounted for the possibility of their results being affected by either the spacing condition or the number of successful repetitions during study periods. there are two forms of implementing spacing in spaced repetition. the first form is absolute spacing. absolute spacing is the measurement of all the trials within the learning and testing periods. an example of this would be that participants would study for a total of thirty trial periods, but the spacing of these trials can either be expanding or uniform. the second form is called relative spacing. relative spacing measures the spacing of trials between each test. an example of this would be if the absolute spacing was thirty, participants would either have expanding intervals (1–5–10–14) or uniform intervals (5–5–5–5–5–5). this is important in measuring whether or not one type of repetition schedule is more beneficial than the other. 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 (absolute spacing).