Study design and participants
This randomized controlled clinical trial was conducted on 66 newly married women with cases in Asad-Abadi and Haft-e-Tir pre-marriage counseling centers in Tabriz. All Iranian couples previously referred to pre-marital centers for pre-marriage tests were selected as sample.
The inclusion criteria were newly married women (1—3 years passed from their marriage), scoring less than 50 in the Hulbert Sexual Assertiveness Index, having at least elementary education, first marriage, and living in a shared house. The exclusion criteria included aged below 18-years, pregnant or breastfeeding women, being candidates for divorce, history of mental disorders, such as depression, suffering from physical diseases, infertility, forced marriage, and addiction of husband or wife.
The sample size was calculated using G-Power software. According to the study of Parva et al. based on the variable of sexual assertiveness and considering M1 = 46.21, with the assumption of 20% increase in the mean score of sexual assertiveness after the intervention (M2= 55.45), SD1= SD2= 10.43, two-sided α = 0.05, and Power = 80%, sample size was obtained 22 in each group. Further, according to the study of Mofid et al.  based on the variable of sexual satisfaction and regarding M1= 92.9, assuming a 15% increase in the mean score of sexual satisfaction following the intervention (M2= 106.8), SD1= SD2= 9.6, two-sided α = 0.05, and Power = 90%, the sample size was estimated to be 12 in each group. Therefore, the total sample size was considered 66 by taking into account the larger sample size for each group (n= 22).
After registering on the website of the Iranian Registry of Clinical Trials (IRCT20170506033834N8), sampling was done in Asad-Abadi and Haft-e-Tir marriage counseling centers in Tabriz from June to March 2021. The researcher (first author) attended the marriage counseling centers, identified as eligible women using the archived information, and after calling and explaining the research objectives, invited those who wanted to participate in the study to attend marriage counseling centers at the appointed time. In the face-to-face session, after completing the questionnaires, women who scored less than 50 in the Hulbert sexual assertiveness index and less than 76 in the Larson sexual satisfaction questionnaire were explained the method of the study. Then, they completed the written informed consent form.
The participants were assigned into CBT-based intervention group, sexual health education receiving group, and control group with a ratio of 1:1:1 by block randomization using Random Allocation Software (RAS) with a block size of 6 and 9. The type of allocation was written on paper and put in sequentially numbered opaque envelopes for the allocation concealment. A non-involved person in the sampling opened the envelopes consecutively. The outcome assessor (the fifth author) was blinded.
One of the intervention groups received CBT based on the ABCDE model during eight 60–90 minute sessions once a week by the third author under the supervision of the fourth author (psychologist). The basic idea behind the ABCDE model is that our emotions and behaviors (C: Consequences) are not directly determined by activating events (A) but rather by the way these events are cognitively processed and evaluated (B: Beliefs). The disputation (D) of the irrational belief into a rational belief results in new effects (E) . The minimum and maximum number of participants in each session was 5 and 7, respectively (Table 1). The other intervention group received 5–7 sessions of sexual health education for 60–90 min, including training and explaining the structure and function of the reproductive system and the stages of the sexual response cycle, familiarizing women with their sexual and reproductive rights, providing examples of sexual violence against women and how to protect themselves, explaining sexually transmitted infections and their prevention methods, genital hygiene, and healthy and responsible sexual behaviors, and training in sexual and communication skills. The third author (sexologist) conducted five educational group sessions and two individual sessions on a per-need basis. The control group did not receive any intervention during the study. Eight weeks after the intervention, members of all three groups filled out the Hulbert sexual assertiveness index and Larson sexual satisfaction questionnaire. In line with ethical considerations, sexual health education sessions were held for the control group after the completion of the research and data analysis.
Data collection tools
The data were collected using the demographic and obstetric characteristics, Hulbert sexual assertiveness index, and Larson sexual satisfaction questionnaire.
Demographic and obstetric characteristics
The demographic and obstetric characteristics include the variables of age, education, occupation, family income, number of intercourses per month, method of contraception, length of marriage, etc.
Hulbert sexual assertiveness index
The Hulbert sexual assertiveness index, developed by Hulbert, was used to measure women’s sexual assertiveness. This 25-item tool is scored on a 5-point Likert scale, ranging from always (0) to never (4). Items 3, 4, 5, 7, 12, 15, 16, 17, 18, 21, 22, and 23 are scored inversely (always = 4 to never = 0). The score range is from 0-100, as 0-33 indicates a low level of sexual assertiveness, 33-50 represents moderate sexual assertiveness, and a score above 50 indicates a high level of sexual assertiveness. The test–retest reliability and internal consistency coefficient of the instrument were obtained 0.86 and 0.89, respectively . In the Iranian version of the instrument, the Cronbach’s alpha coefficient and Intraclass Correlation Coefficient (ICC) were reported to be 0.92 and 0.91, respectively .
Larson sexual satisfaction questionnaire
The sexual satisfaction was assessed using the Larson sexual satisfaction questionnaire, developed by Larson et al. . The questionnaire consists of 25 items and 4 dimensions, including libido, sexual attitude, quality of sexual life, and sexual adjustment. Each item is scored on a 5-point Likert scale, ranging from never = 1 to always = 5. Items 4—9, 11, 14, 15, 18, 20, 24, and 25 are inversely scored from 5 to 1, respectively . The minimum possible score is 25 and the maximum is 125, as a score less than 50 reflects a lack of sexual satisfaction, 51–75 indicates low satisfaction, 76–100 displays moderate satisfaction, and more than 100 demonstrates high sexual satisfaction. In the Persian version of the instrument, the Cronbach’s alpha coefficient and ICC were reported as 0.9 and 0.86, respectively .
The data were analyzed using SPSS25software and Shapiro–Wilk test was employed to assess the data normality. The mean score of sexual assertiveness and sexual satisfaction was compared among the three groups using ANOVA test before the intervention and ANCOVA test after the intervention by controlling the effect of the baseline score.