Technical Manual - Renaissance Learning

Psychometric Research Supporting STAR Early Literacy EnterpriseItem CalibrationThe objectives of the Calibration Study were to:Collect sufficient response data to allow IRT item parameters to be estimatedfor all 2,929 STAR Early Literacy items.Conduct preliminary research into the psychometric reliability of STAR EarlyLiteracy tests, using a test-retest design.Assess the degree of relationship between STAR Early Literacy scores and astandardized reading achievement test.In support of the first objective, provisions were made during forms design tofacilitate expressing all IRT item parameters on a common scale. To that end,some of the test items were used as “anchor items”—items common to two ormore forms that are used to facilitate linking all items to the common scale. Twokinds of anchoring were used: 1) horizontal (form-to-form) anchoring, and 2)vertical (level-to-level) anchoring.Horizontal anchoring: The purpose of horizontal anchoring is to place all items ata given level on the same scale, regardless of differences among the forms at thatlevel. To accomplish that, several items appeared in all forms at a given level.These horizontal anchor items were chosen to be representative of the sevencontent domains and to be appropriate for the grade level.Vertical anchoring: The purpose of vertical anchoring is to place items atadjacent levels on the same scale. To accomplish that, a number of items wereadministered at each of two adjacent levels: A and B, or B and C. As much aspossible, the vertical anchor items were chosen to be appropriate at both thelower and higher levels at which they were used.Table 12 depicts the distribution of the three types of items within STAR EarlyLiteracy calibration test forms. The distribution differs from one level to another.The three item types are horizontal anchor items, vertical anchor items, andunique (non-anchor) items.Table 12:Number of Anchor Items and Unique Items in Each 40-Item Test Form,by LevelItem TypeLevel APre-K & KLevel BGrade 1Level CGrades 2 & 3Horizontal anchor items 5 7 5Vertical anchor items 5 11 6Unique items 30 22 29Total 40 40 40STAR Early LiteracyTechnical Manual40