Data from: Transcultural adaptation: a validity and reliability study of the Tendinopathy Severity Assessment–Achilles (TENDINS-A) for the Spanish population in accordance with the COSMIN recommendations

This dataset accompanies the study "Cross-cultural adaptation and psychometric validation of the Spanish version of the TENDINS-A questionnaire (TENDINS-A-SP)". It contains anonymized data from 105 Spanish-speaking adults with Achilles tendinopathy (51.4% female; mean age 40.4 years). The data include: Participant characteristics: age, sex, height, weight, body mass index (BMI), and physical activity level. Patient-reported outcome measures: TENDINS-A-SP item and total scores, together with FAOS-SP and VISA-A-SP scores used for convergent validity assessment. Test–retest measurements: repeated TENDINS-A-SP assessments collected 48 hours apart for reliability analysis. The dataset was used to evaluate the psychometric properties of the TENDINS-A-SP, including structural validity, convergent validity, internal consistency, test–retest reliability, measurement error, and measurement invariance. Exploratory and confirmatory factor analyses supported a three-factor structure (pain, symptoms, and function). The questionnaire demonstrated excellent reliability (ICC = 0.960), high internal consistency, and adequate convergent validity with FAOS-SP and VISA-A-SP. This dataset supports reproducibility of the validation study, secondary psychometric analyses, cross-cultural adaptation research, and future studies involving patient-reported outcome measures for Achilles tendinopathy. It may also be useful for methodological research on factor analysis, reliability testing, and measurement invariance in health-related questionnaires.