Desain Instrumen Diagnostik Berbasis Model IRT Materi Sistem Persamaan Linier Perguruan Tinggi - Irwanto, Jesi (Penerbit Widina, Widina Media Utama, 2025)
Students' understanding of the Two-Variable Linear Equation System is still relatively low, so a diagnostic instrument is needed that is able to identify conceptual weaknesses accurately. This study aims to design a diagnostic instrument based on the Item Response Theory (IRT) model of three-parameter logistic (3PL) on the material. The research method used is a quantitative approach with the stages of designing question grids, expert validation, trials on 80 students, and data analysis using R Studio software. The results showed that 21 of the 25 questions met the validity criteria and unidimensionality assumptions. The instrument has high reliability (0.92) and is able to map students' abilities into three main categories. This fact shows that the IRT model is effective in developing diagnostic instruments and can help lecturers design data-based learning strategies to improve understanding of the two variables equations system concept in higher education. this instrument provides educators with a reliable tool for identifying learning gaps, enabling more targeted interventions and personalized support for students struggling with linear equation systems.ABSTRAKPemahaman mahasiswa terhadap Sistem Persamaan Linier Dua Variabel (SPLDV) masih tergolong rendah, sehingga diperlukan instrumen diagnostik yang mampu mengidentifikasi kelemahan konsep secara tepat. Penelitian ini bertujuan untuk merancang instrumen diagnostik berbasis Item Response Theory (IRT) model tiga parameter logistik (3PL) pada materi SPLDV. Metode penelitian yang digunakan adalah pendekatan kuantitatif dengan tahapan perancangan kisi-kisi soal, validasi ahli, uji coba terhadap 80 mahasiswa, dan analisis data menggunakan perangkat lunak R Studio. Hasil penelitian menunjukkan bahwa 21 dari 25 butir soal memenuhi kriteria validitas dan asumsi unidimensionalitas. Instrumen memiliki reliabilitas tinggi (0.92) serta mampu memetakan kemampuan mahasiswa dalam tiga kategori utama. Fakta ini menunjukkan bahwa model IRT efektif digunakan dalam pengembangan instrumen diagnostik dan dapat membantu dosen merancang strategi pembelajaran berbasis data untuk meningkatkan pemahaman konsep SPLDV di perguruan tinggi.