The study we present in this paper is an in-depth international comparative investigation of proficiency in the related concepts of ratio, proportion and percent based on TIMSS 2011 data. A secondary analysis is proposed to analyze a subset of items from TIMSS 2011 addressing the related concepts within the multiplicative conceptual field (MCF) for a subset of South African learners who participated in the study. Following on the theoretical basis of a previous research project, and based on Rasch measurement theory, an in-depth analysis of items and learner proficiency locations will be conducted to further understand concepts and skills within the MCF. In addition it is proposed that the analysis of an equivalent subset of the learners from England and Australia will verify whether the outcomes of the South African study can be generalized to other cultural settings. It is expected that the outcomes will inform the mathematics education community, in particular those researchers focusing on the pivotal area of ratio, proportion and percent. The application of this competence model may also be of interest to researchers involved in large scale assessment as this model will extend the use and relevance of the data generated by these studies.