Standardized Letters of Recommendation in Medical Residency Selection, a Critical Review of the Recent Literature

Standardized Letters of Recommendation (SLORs) were introduced in the United States and Canada to address limitations of narrative letters in residency selection by improving objectivity, comparability, and reliability. This review evaluates their structure, performance, and broader adoption across regions. This narrative review synthesizes the literature published between 1995 and 2025, including survey-based studies, a systematic review, and specialty-specific analyses. Key domains examined include SLOR structure, predictive validity, score inflation, interrater reliability, correlation with objective metrics, and potential bias. SLORs are widely used across multiple North American specialties but remain rare in Europe, with limited implementation such as in Swiss pediatrics. The summative ranking component consistently shows the strongest association with match outcomes, whereas other domains demonstrate limited discriminatory value due to ceiling effects and score inflation. Interrater reliability remains suboptimal, and correlations with objective metrics such as USMLE scores are weak. Although major demographic biases are not evident, local applicants and those with distinctions tend to receive more favorable evaluations. SLORs represent an improvement over narrative letters but require refinement. Enhancing rating scales, strengthening rater training, and developing more detailed structured assessments may improve their reliability and utility as evaluation tools.