AIMS: To assess the measurement properties of the Ms. Olsen test for registered nurses and assistant nurses, respectively, and suggest cut-off points between competence levels. DESIGN: Cross-sectional study. The results were analysed by implementing the Rasch Measurement Theory. METHODS: Nursing staff working in various health care settings participated (n = 757). To measure the competence of nursing staff in clinical decision-making, a 19-item scale from the Nursing Older People-Competence Evaluation Tool-the 'Ms. Olsen test'-was used. Data were collected in October 2017, 2018 and 2019. RESULTS: The Ms. Olsen test showed reasonably good measurement properties for registered nurses and assistant nurses respectively. Results show slightly better measurement properties for registered nurses than for assistant nurses. The cut-off for registered nurses, 0.62, corresponds to managing approximately two-thirds of the items while, for assistant nurses, the cut-off of 0.01 corresponds to managing approximately half of the items. CONCLUSION: The Ms. Olsen test is a short (7- to 10-min) test measuring competence in clinical decision-making among nursing staff working in older people nursing. Despite reasonably good measurement properties, this should be considered an initial validation in the development of a short test for assessing clinical decision-making among nursing staff in various health care setting. IMPACT: Several scales aiming to measure nursing competence have been developed over the last decade, but measurement properties (beyond classical test theory) are seldom evaluated, few scales concern other staff groups than registered nurses and few scales have proposed or established cut-offs for safe practice. The Ms. Olsen test is a short test of clinical decision-making that demonstrates reasonably good measurement properties. Cut-off points for registered nurses and assistant nurses were established. The Ms. Olsen test may be used to measure and evaluate competence in clinical decision-making among nursing staff working in older people nursing and educational settings.