Conceptualisation and application of implementation strength in public health programmes within health systems: a systematic review.

backgroundImplementation strength (IS), a cardinal concept in the field of implementation science, is used to assess how the implementation of health services and specific health programme influences health outcomes. It offers a unique opportunity to determine how much implementation effort is required to achieve a meaningful level of change in outcomes. Despite its growing use, a lack of conceptual clarity has led to inconsistent measurement and sub-optimal application. We explored how IS is defined, measured, and associated with outcomes, and proposed a set of recommendations for its future use.

methodsUsing an integrated approach combining systematic review and principles of concept analysis, a comprehensive search of PubMed, Scopus, ERIC, and Google Scholar was conducted up to July, 2025. Peer-reviewed theoretical and empirical studies conducted within health systems-regardless of study design, location, or population were eligible for inclusion. JBI tools were used for quality assessment. Data were synthesised using a content analysis approach.

findingsIS is often vaguely defined, with mismatches between its definitions and how it is measured. The concept has primarily been applied to health programmes implemented in real-life settings; however, no study has applied it to routine healthcare services. Studies conceptually-grounded in 2011-13 IS guidance differed notably from their counterparts: they used fewer but more relevant indicators, advanced statistical methods for composite indices, and examined dose-response relationship. Yet, most studies overlooked broader programme components outlined in the WHO monitoring & evaluation framework. Measurement practices varied widely and often conflating IS with implementation fidelity. Few studies analysed the relationship between IS and outcomes, but those that did reported a strong positive association. While half of the studies were of high quality, most lacked a reliable and valid composite IS index.

conclusionOur review comprehensively mapped existing confusion surrounding the conceptualisation of IS, identified shortcomings in its application, and offers a scientifically grounded resolution aimed at standardising its conceptualization and application, thereby enabling consistent comparisons across settings. Strong evidence of a positive relationship between IS and health system outcomes reinforces the value and potential of this approach in strengthening health systems. Future research should focus on developing standardised and validated IS indices across health themes, along with effective and feasible approaches for integrating them into routine health systems for use by health administrators. CLINICAL TRIAL NUMBER: Not applicable.