A critical appraisal tool for interdisciplinary study designs: Conceptual grounding and application in healthy ageing research.

Interdisciplinary research often employs heterogeneous study designs that cannot be consistently addressed by existing quality appraisal frameworks. Established tools (CASP, JBI, EPHPP, STROBE) provide robust criteria, but no single framework adequately captures the methodological diversity typical of interdisciplinary work. Originating in a systematic review of 55 empirical studies on healthy ageing (Piriu et al., 2025), this article introduces the Nine-Item Quality Appraisal Toolkit (9-QuAT), a methodological innovation for critically assessing quality across diverse interdisciplinary study designs. The toolkit incorporates criteria from established frameworks, ensuring conceptual grounding, and extends them to include dimensions such as integration of methods, sample representativeness, and contribution to knowledge. Each criterion is operationalized in a binary scoring system, providing a structured yet flexible approach that enables reproducible and transparent assessment across heterogeneous designs, including mixed-methods, observational, descriptive, and exploratory studies. In doing so, the tool offers both a multidimensional research evaluation method and a transferable framework for interdisciplinary health and social research where traditional appraisal tools fall short. The article contributes along the following lines:•Introduces a nine-item binary scoring toolkit for appraising interdisciplinary study designs.•Extends established appraisal frameworks to capture interdisciplinarity and translational relevance.•Demonstrates reliability, conceptual validity, and transferability across domains.