Alternate Form Reliability of the Revised Peabody Picture Vocabulary Test for Head Start Children
A review of the reliability data of the Peabody Picture Vocabulary Test (3) indicates that the median coefficient for preschool children, including head start programs, was .64 and .72 for all-aged subjects (2) which suggests that the Peabody Test was less reliable for preschool children. The present study investigated the alternate form reliability of the Peabody Picrure Vocabulary ~est-~evised' (4) with head start children. Forms L and M were administered in counterbalanced order to 39 males ranging in age from 45 to 68 mo. (M = 57.23 mo., SD = 7.42) and 40 females ranging in age from 46 to 75 mo. (M = 57.08 mo., SD = 7.80). A time period of three to seven days elapsed between administrations. All subjects were given both forms by the same trained examiner. The range of standard scores for Form L was 45 to 128, M = 89.51, SD = 14.13; for Form M range was 59 to 127, M = 93.73, SD = 13.04. A significant difference between means was indicated by a t test for correlated data (t = -4.22, fi < .001) which suggests that the standard score equivalent for head start children is significantly higher on Form M than Form L. However, in a practical sense the mean difference between forms is not important as an examiner should report the true score for form used which is estimated by using the obtained score and standard error of measurement. Sex differences were nonsignificant; on Form L females' M = 89.08, SD = 15.42 ' and males' M = 89.95, SD = 12.87 (t = .27); on Form M females' M = 91.43, SD = 12.64 and males' M = 96.10, SD = 13.18 (t = 1.61). Pearson product-moment correlation of .79 between forms was substantial and significant (p < ,001). This finding is consistent with the immediate rerest reliability coefficient for alternate forms using standard score equjvalencs for ages 3-0 to 5-11 which have a median coefficient of .76 and .79 for subjects of all ages as cited by Dunn (4, p. 56). Further, results support use of the Peabody Picture Vocabulary Test-Revised as a consistent measure for head start children since these values compare favorably with the reliability coefficients of the standardization sample. The obtained correlation is lower than is desirable for reliability coefficients which usually fall in the 30's or .Yo's (1, p. 109).