Replication of Psychometric Properties of the FSFI and Validation of a Modified Version (FSFI-LL) Assessing Lifelong Sexual Function in an Unselected Sample of Females

Abstract

The 19-item Female Sexual Function Index (FSFI) is an easy-to-administer self-report questionnaire, allowing multidimensional assessment of female sexual function and female sexual dysfunction (FSD) over the past 4 weeks. However, studies aiming to dissect the underlying pathoetiology-especially biophysiological factors-often require assessment of sexual function over a broader time frame. The purpose of this study was to develop a modified version of the widely used FSFI which allows assessment of women's lifelong sexual function-the FSFI-LL-and to evaluate the psychometric properties and aptness of this new version. A total of 1,589 unselected female twins from the TwinsUK registry completed both original and new versions of the FSFI. After applying exclusion criteria, 1,489 women were eligible for this study. Reliability was tested using Cronbach's alpha coefficient. Construct validity was evaluated by exploratory factor analysis and confirmatory factor analysis (CFA). Domain response differences between the original FSFI and the FSFI-LL were assessed using unpaired t-tests. The modified FSFI-LL showed adequate internal consistency reliabilities for all six dimensions and the total score (Cronbach's α = 0.79 - 0.92). Principal component analysis resulted in a best fitting five-factor solution. CFA confirmed the underlying domain structure to be same as for the FSFI, supporting the factorial validity of the modified questionnaire. In addition, successful replication of the psychometric properties of the original FSFI was demonstrated. The results provide evidence of good reliability and validity of the FSFI-LL. This modified version therefore represents a suitable tool for screening lifelong sexual function in women and can be applied in trials investigating etiological factors contributing to more enduring patterns of FSD.