Nuancing the continuum from ideal to real-world implementation: a letter to the editor on Nilsen et al.

Nilsen et al.'s (Implement Sci Commun 6:90, 2025) proposal to distinguish between implementation efficacy and effectiveness, and to situate implementation studies along a continuum from ideal to real-world conditions, offers a valuable conceptual advance. In this commentary, we acknowledge the contribution of their debate while highlighting potential limitations of applying a single-axis continuum to a field heavily characterized by contextual complexity. Drawing from decades of healthcare quality improvement, we argue that implementation interventions often blend efficacy-like and effectiveness-like elements, making neat classification difficult. We further suggest that oversimplification risks obscuring the realities of organizational change. Instead, we propose a double-axis model that considers both the implementation intervention and the context in which it unfolds. Economic evaluation likewise requires nuanced approaches that go beyond their proposed continuum indicator tool ("Implementation PRECIS"). To constructively extend Nilsen et al.'s contribution, we advocate for integration of the tool with existing approaches to evaluation, co-production with stakeholders, and empirical validation across diverse settings. While no implementation endeavor is ideal, advancing discourse around how efficacy and effectiveness are conceptualized can support more pragmatic, context-responsive, and sustainable improvements in healthcare.