In most reliability studies, the precision of a reliability estimate varies inversely with the number of examinees (sample size). Thus, to achieve a given level of accuracy, some minimum sample size is required. An approximation for this minimum size may be made if some reasonable assumptions regarding the mean and standard deviation of the test…

The optimal test length, using predictive validity as a criterion, depends on two major conditions: the appropriate item-difficulty rather than the total number of items, and the method used in scoring the test. These conclusions were reached when responses to a 100-item multi-level test of reading comprehension from 136 non-native speakers of…