The purpose of this study was to examine the effect of selected student profile variables in the 2005 American College Test (ACT) on academic performance of Mississippi high school graduates as measured by the subscales in the ACT. The sample consisted of 16,779 high school graduates that completed the ACT in Mississippi in 2005. The variables that were studied were the ACT subscores: English, mathematics, reading, and science reasoning subscales; race/ethnicity, size of graduating high school class, high school curriculum, and gender, which were completed on the student profile section when the student registered for the ACT. Analysis of variance (ANOVA) and multiple regression analysis at the .05 alpha level, and Means were used to test the statistical significance of the effect of each variable on the ACT subscores. The findings resulted in a statistically significant difference occurring in all four predictor variables: race/ethnicity, size of graduating high school class, high school curriculum, and gender; except no statistically significant difference in gender in the ACT subscore of English and reading. Only two variables explained 40% of the variance of the English ACT subscore: race and ethnicity, and class size. Three variables explained 52% of the variance of the math ACT subscore: (a) race and ethnicity, (b) class size, and (c) gender. All four variables explained 36 % of the variance of the science reasoning ACT subscore. The conclusions drawn from this study were that there were statistically significant differences in the ACT subscore means among the different racial and ethnic groups of students. The mean scores were the lowest for the race and ethnicity variable in the African American background. The lowest ACT subscore mean was in the 399 or below class size, and the highest ACT subscore mean was in the 900 or more class size. The college preparatory program of study scored higher mean scores than the lower ranking other or general and business/vocational program of study, respectively. Overall, males scored higher on the ACT subscores than the females with females outranking males in English. These were found to be probable predictors of success on the ACT.

College admission tests are of great importance for admissions systems in general and for candidates in particular. The SweSAT (Högskoleprovet in Swedish) has been used for college admission in Sweden for more than 30 years, and today it is alongside with the upper-secondary school GPA the most widely used instrument for selection of college applicants. Because of the importance that is placed on the SweSAT, it is essential that the scores are reliable and that the interpretations and uses of the scores are valid. The main purpose of this thesis was therefore to examine some assumptions that are of importance for the validity of the interpretation and use of SweSAT scores. The argument-based approach to validation was used as the framework for the evaluation of these assumptions.The thesis consists of four papers and an extensive introduction with summaries of the papers. The first three papers examine assumptions that are relevant for the use of SweSAT scores for admission decisions, while the fourth paper examines an assumption that is relevant for the use of SweSAT scores for providing diagnostic information. The first paper is a review of predictive validity studies that have been performed on the SweSAT. The general conclusion from the review is that the predictive validity of SweSAT scores varies greatly among study programs, and that there are many problematic issues related to the methodology of the predictive validity studies. The second paper focuses on an assumption underlying the current SweSAT equating design, namely that the groups taking different forms of the test have equal abilities. The results show that this assumption is highly problematic, and consequently a more appropriate equating design should be applied when equating SweSAT scores. The third paper examines the effect of textual item revisions on item statistics and preequating outcomes, using data from the SweSAT data sufficiency subtest. The results show that most kinds of revisions have a significant effect on both p-values and point-biserial correlations, and as a consequence the preequating outcomes are affected negatively. The fourth paper examines whether there is added value in reporting subtest scores rather than just the total score to the test-takers. Using a method derived from classical test theory, the results show that all observed subscores are better predictors of the true subscores than is the observed total score, with the exception of the Swedish reading comprehension subtest. That is, the subscores contain information that the test-takers can use for remedial studies and hence there is added value in reporting the subscores. The general conclusion from the thesis as a whole is that the interpretations and use of SweSAT scores are based on several questionable assumptions, but also that the interpretations and uses are supported by a great deal of validity evidence.

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Validity is a crucial part of all forms of measurement, and especially in instruments that are high-stakes to the test takers. The aim of this thesis was to examine theory and validity evidence for a recently revised large-scale instrument used for selection to higher education in Sweden, the Swedish Scholastic Assessment Test (SweSAT), as well as identify threats to its validity. Previous versions of the SweSAT have been intensely studied but when it was revised in 2011, further research was needed to strengthen the validity arguments for the test. The validity approach suggested in the most recent version of the Standards for education and psychological testing, in which the theoretical basis and five sources of validity evidence are the key aspects of validity, was adopted in this thesis. The four studies that are presented in this thesis focus on different aspects of the SweSAT, including theory, score reporting, item functioning and linking of test forms. These studies examine validity evidence from four of the five sources of validity: evidence based on test content, response processes, internal structure and consequences of testing. The results from the thesis as a whole show that there is validity evidence that supports some of the validity arguments for the intended interpretations and uses of SweSAT scores, and that there are potential threats to validity that require further attention. Empirical evidence supports the two-dimensional structure of the construct scholastic proficiency, but the construct requires a more thorough definition in order to better examine validity evidence based on content and consequences for test takers. Section scores provide more information about test takers' strengths and weaknesses than what is already provided by the total score and can therefore be reported, but subtest scores do not provide additional information and should not be reported. All four quantitative subtests, as well as the Swedish reading comprehension subtest, are essentially free of differential item functioning (DIF) but there is moderate DIF that could be bias in two of the four verbal subtests. Finally, the equating procedure, although it appears to be appropriate, needs to be examined further in order to determine whether it is the best practice available or not for the SweSAT. Some of the results in this thesis are specific to the SweSAT because only SweSAT data was used but the design of the studies and the methods that were applied serve as practical examples of validating a test and are therefore likely useful to different populations of people involved in test development, test use and psychometric research. Suggestions for further research include: (1) a study to create a more clear and elaborate definition of the construct, scholastic proficiency; (2) a large and empirically focused study of subscore value in the SweSAT using repeat test takers and applying Haberman’s method along with recently proposed effect size measures; (3) a cross-validation DIF-study using more recently administered test forms; (4) a study that examines the causes for the recurring score differences between women and men on the SweSAT; and (5) a study that re-examines the best practice for equating the current version of the SweSAT, using simulated data in addition to empirical data.