How to deal with the common mistakes in applying Female Sexual Function Index (FSFI)

Dear Editor

With the increasing expansion of studies in the field of women's sexual health, today various studies are being conducted using valid and standard questionnaires. The Female Sexual Function Index (FSFI) is a 19-item self-report questionnaire that measures six dimensions of female sexual function including desire, arousal, lubrication, orgasm, satisfaction and pain. Calculating the score in this tool is a little different from other questionnaires because after calculating the score of each dimension as a sum of scores, the score should be multiplied by the specific coefficient of the same dimension (desire (0.6), arousal and lubrication (0.3), orgasm, satisfaction, and pain (0.4)). This is done to give the same weight to different dimensions of the scale (1).

 Ziaei et al. in their study entitled the relationship between sexual self-concept and sexual function in women of reproductive age (2), reported that the range of mean scores of each female sexual function dimension is between 6.27 and 16.46, which is different from the measurable range in each dimension (0 to 6). The reported total score (68) was also outside the measurable range of the scale (2-26) (1). Although Ziaei et al. referred to the necessity of weighting of scale scores in introducing FSFI, in the report of the findings, the raw scores of each dimension were not weighed. This is one of the most common mistakes in FSFI scoring and interpretation (3).

Another noteworthy point is that in FSFI, a higher score in each dimension indicates a better sexual function. For example, a higher score in the dimension of ​​pain means less pain or no pain during sex (3). Therefore, the direct relationship between sexual anxiety and pain means that with increasing sexual anxiety, pain decreases, while Ziaei et al. reported that increased sexual anxiety is associated with increased pain (2).

In addition, there is a misuse of epidemiologic terms in the report of the results. In mathematical terms, a correlation coefficient provides a measure of the strength and direction of the relationship between two variables. Pearson correlation coefficient only measures linear relationships, while spearman correlation coefficient measures monotonic relationships. Both correlations coefficient which are denoted by r can range from -1 to +1. When r equals -1 indicates a perfect negative or inverse relationship and when r equals +1 indicates a perfect positive relationship (4). So, the authors of aforementioned study, used the term “indirect correlation” which means a nonlinear correlation instead of negative or inverse correlation to describe the relationship between the two variables of sexual anxiety and intercourse pain measured by Spearman correlation coefficient (5).

In conclusion, the lessons learned from these issues include a) the researchers must pay attention to the guidelines of questionnaires to collect, analyze and interpret data correctly and b) the correct usage of statistical and epidemiological terms is critical in interpretation of the results.

In order to avoid possible future mistakes in using the results of above mentioned study by other researchers, the first author of the article (T.Z) reanalyzed data and edited the article. The revised article along with the editorial letter were send to the Journal of Midwifery and Reproductive Health (JMRH).

Conflicts of interest

Authors declared no conflicts of interest.