Item Analysis of an Instrument to Measure Chemistry Students' Critical Thinking Skills Based on Science, Technology, Engineering and Mathematics (STEM) on Solubility and Solubility Product (KSP) material using the Rasch model

In STEM-based learning students use science, technology, engineering, and mathematics in real interactions that connect schools, the world of work, and the global world to develop STEM literacy that enables students to be able to compete in the 21st century. The STEM learning approach by integrating its four components is able to produce students 'thinking activities that are useful to help raise students' critsical thinking which is characterized by the ability to solve problems, make decisions, analyze assumptions, evaluate, and conduct investigations. Evaluation tools have an important role in the learning process. The purpose of this study was to analyze critical thinking skill items on solubility and solubility product (Ksp) material using the Rasch model in terms of validity, reliability, and item difficulty level. The method used is descriptive quantitative with 106 participants students from three High School in Surakarta. Data collection techniques in this study are documentation. The number of items as many as 30 questions obtained results, namely the validity of the suitability level of items that are fit as many as 30 questions. Student reliability 0.44 is weak, item reliability 0.97 is good and reliability between students with item 0.47 is sufficient. The level of difficulty of the questions is very difficult, difficult and easy is dominated by questions categorized as difficult. In conclusion, the analysis of critical thinking skill items on solubility and solubility product (Ksp) material using the Rasch model is valid, reliable, and the level of difficulty items was very good. So the questions that have been analyzed can be used to determine critical thinking skills.