Assessing achievement is a complex task due to its dependence on multiple factors and the hierarchical structure of educational data, yet surveys like TIMSS offer valuable insights into its determining factors like students' mathematics anxiety. However, disregarding the nested structure of data and ignoring the assumptions of models causes poor…

Multilevel international data have been released from the Third International Mathematics and Science Study (TIMSS), providing an opportunity to apply multilevel modeling techniques in educational research. In this paper, TIMSS factors are classified in fixed and random categories according to the project design. Classifying fixed and random…