Analysis of the psychometric evidence of the Female Sexual Function Index (FSFI) & measurement invariance across relationship status & age generations in a Chilean sample

Background: Inconsistencies in the Female Sexual Function Index (FSFI) factor structure and current research and clinical guidelines highlight the need for continued exploration of its psychometric evidence. Furthermore, only one study has assessed its measurement invariance (MI), while the only FSFI psychometric study conducted in Chile lacks quality and representativity. Aim: Therefore, this study aimed to evaluate the psychometric properties of the FSFI (ie, structural and convergent validity, and reliability) in a Chilean sample of women, while also examining MI across relationship status and age groups. Method: A sample of 2595 sexually active adult women (Mage = 32.10, SDage = 10) was derived from a broader Chilean study (Chilean National Sex and Sexuality Study). We used a confirmatory factor analysis to determine its structural validity, sexual satisfaction (SS) dimensions to establish its convergent validity, and Cronbach's alpha and McDonald's omega to assess the reliability of its scores. Outcomes: Measures of goodness-of-fit. Results: Confirmatory factor analysis supported a six-factor structure. Internal consistency indices for all FSFI dimensions ranged from good to excellent. MI was achieved across socio-demographic variables at the factor covariance level. Convergent validity indicated modest-to-moderate effects in satisfaction differences based on relationship status. Among other findings, Chilean women in a relationship had significantly higher satisfaction with their sexual communication and compatibility than those who were single, which is consistent with previous findings. Meanwhile, women at risk of experiencing sexual problems scored significantly lower across all SS dimensions than those not at risk. Clinical Implications: This study provides evidence that the FSFI is a valid, reliable, and invariant tool for the clinical practice in the sexual health of Spanish-speaking Latino Americans, especially that of Chilean women's sexual function (SF) and problems. Strengths & Limitations: This study provided a comprehensive analysis of the FSFI's psychometric validity evidence, demonstrating its reliability and validity across diverse Chilean women while also offering its first assessment of MI and confirming its suitability for clinical and research use in Spanish-speaking Latino women. Conversely, this study's main caveat lies in having a predominantly younger, cisgender, and heterosexual sample. Conclusion: Nevertheless, this study's findings support the FSFI as a valuable research tool for female SF and well-being, particularly within the Chilean population. This study significantly expands the applicability of the FSFI and underscores its MI across sociodemographic factors, as well as its applicability in the Spanish-speaking Latino-American sociodemographic context, particularly the Chilean one.