Participants and procedures
This cross-sectional validation study was applied in Sari city, the capital of Mazandaran province, the north of Iran, from February to June 2017. In the present study, the sample size was estimated based on the number of items in the scale multiplying by 10, as suggested (24×10=240). The most commonly used minimum sample size estimation method in structural equation modeling (SEM) is the ‘10-times rule’ procedure. The '10‐times rule' has been preferred due to its simplicity of use (35, 36). In all, 480 pregnant women participated in EFA (240 pregnant women) and CFA (240 pregnant women). Data for this study come from pregnant women who attended a Baghban specialist clinic, public health care centers, and private clinics of gynecologists in Sari city, the capital of Mazandaran province. Women were chosen using a multi-stage random sampling method. The first step of the sampling method was aimed to select samples from all regions. To this end, a list of public health care centers and gynecological clinics were provided. Subsequently, in proportion to the number of target groups in each of the public and private service centers, the number of samples required was consecutively entered into the study via a simple sampling method.
The inclusion criteria were being pregnant women with gestational age from seventh to ninth month and interested in participating in the study. Exclusion criteria were a lack of willingness, having a mental disease, or having a specific physical condition like having complete placenta Previa that was not possible to cooperate and complete the questionnaire. The demographic characteristics of the women included age, level of education, and employment status. Data collection approaches were based on nameless scales that were completed by an expert interviewer. The interviewer received guidelines for similar completing the scales after attending a training session.
The scale development process
This study performed for developing an instrument to measure the intention of pregnant women for the cesarean section delivery method. Scale development was made following stages. The first stage was done to specify the content domain of a construct. In this stage, it was done interviews with the experts/pregnant women and the review of literature in this background relating to the TRA (37-41) for developing an item pool and content domain. The main dependent variable in the present analysis was the cesarean delivery method. Besides, the independent variables include five factors, organized into logical framework counting (a) behavioral beliefs, (b) evaluation of behavioral outcomes, (c) motivation to comply, (d) normative beliefs, and (e) behavioral intention. The item pool contained 39 items at this point. It was tried making clear the content of the items and deleted extra items via discussion. The principal researcher and other team members read items and removed extra items. To the end, the first draft of the instrument was developed and consisted of 27 items. In the second stage, the psychometric properties of the Iranian version of the theory-based intention to cesarean section (IR-TBICS) scale were done to assess the validity and reliability of a new scale.
Content validity:
It is a wide-ranging review by a panel of experts to determine whether items sufficiently contain the subject aimed at assessing them. It is a crucial phase for developing a tool and a method for linking abstract notions with tangible and measurable indexes. The expert panel consisted of 10 specialists in health education and promotion, gynecologist, and instrumentalist. Qualitative content validity was assessed according to the wording, scaling, grammar, and item allocation indices (42). All items were tested, and the expert panel's suggestions were put into the scale. We applied the content validity index (CVI) and content validity ratio (CVR) for reaching the quantitative content validity of a new scale. For measuring CVR, the expert panel was questioned to assess each item through a 3-point Likert scale including, 1 = essential, 2 = useful but not essential, and 3 = unessential. The CVR for each item was assessed using formula CVR = [Ne - (N/2)] ÷ (N/2) (Ne is the number of panelists demonstrating "essential" for each specific item and N is the total number of the expert panel). The numeric value of CVR is identified by the Lawshe table. Based on Lawshe's table (43), items with a CVR score of .62 or above were chosen (42). For the CVI, according to Waltz and Bausell (44) reference, the same panel was questioned to assess the items based on a 4-point Likert scale on ‘relevancy,' ‘clarity,' and ‘simplicity.' The number of those stated the item as relevant or clear (rating 3 or 4) was allocated by the number of a content expert panel. A CVI score of .79 or above was measured acceptable (43, 45).
Face validity:
Face validity is an assessment of laywomen in understanding and knowing an instrument. In this step, both quantitative and qualitative approaches were used. For the quantitative step, ten pregnant women were questioned to assess the instrument and degree the importance of items on a 5-point Liker scale for evaluating 'Item Impact Score' (Impact Score = Frequency (%) × Importance). The impact score of equal to 1.5 or more was measured acceptable, as mentioned (46). For the qualitative step, the same pregnant women were questioned about the ‘relevancy,' ‘ambiguity,' and ‘difficulty' of each item; and some minor modifications were performed to the primary instrument.
A pre-final version of the instrument: following the reflection of the above methods, the pre-final version of the instrument containing 24 items was created for the next phases (construct validity and reliability of the IR-TBICS scale).
Statistical analysis
Construct validity
The construct validity of the IR-TBICS scale was done using both exploratory (EFA) and confirmatory factor analyses (CFA).
The main study and data collection
A cross-sectional study was planned to assess the psychometric properties of the IR-TBICS scale. A consecutive sample of the pregnant women was recruited from Baghban specialist clinic, public health care centers, and private clinics of gynecologists affiliated to Mazandaran University of Medical Sciences.
a) Exploratory factor analysis (EFA):
A sample of 240 pregnant women completed the IR-TBICS scale, and its factor structure was extracted by the principal component analysis with varimax rotation. Bartlett's Test of Sphericity and Kaiser-Meyer-Olkin (KMO) were applied to assess the suitability of the sample for the factor analysis. Eigenvalues above one and scree plot were conducted for identifying the number of factors. Factor loadings equal/greater than 0.4 were considered appropriate (47).
b) Confirmatory factor analysis (CFA):
A separate sample of 240 pregnant women completed the IR-TBICS scale, and factor analysis was conducted to measure the model fitness. As suggested several fit indices counting relative Chi-square (χ2/df), goodness of fit index (GFI), Normed Fit Index (NFI), Non-Normed Fit Index (NNFI), Standardized Root Mean Square Residual (SRMR), Comparative Fit Index (CFI), and Root Mean Square Error of Approximation (RMSEA) were conducted (48, 49). Relative Chi-square is the ratio of chi-square to degrees of freedom, and its suggested reference value is less than three for accepting the fitness of the model. The value for GFI, CFI, NFI, and NNFI could range between ‘0 to 1' and values closer to 1 are revealing of data fitness (50, 51). An RMSEA ranged .08 to .10 displays an average fit, and less than .08 identifies a good fit (49). The satisfactory value for SRMR is below.10 where values under .08 display satisfactory fit and values less than .05 show good fit (52).
Reliability
Cronbach's α coefficient assessed the internal consistency of the IR-TBICS scale. Cronbach's α coefficient of equal to 0.7 and more were identified acceptable (53). Floor and ceiling effects were determined as present if more than 15 % of the responders attained the lowest or highest possible IR-TBICS scale total score (49). Furthermore, a sub-sample of pregnant women (n = 25) completed the IR-TBICS scale twice with a 2-weeks interval for testing the stability of the IR-TBICS scale by computing Intraclass Correlation Coefficient (ICC) where the ICC of 0.4 or more was reflected acceptable (54). All statistical analyses, except CFA, were done using the SPSS V.22.0 (55). The CFA was done using the AMOS software V.22.0 for Windows (56).
Scoring
In the final version of the IR-TBICS, for each construct, a minimum of three and a maximum of seven items were generated. In the present study, behavioral beliefs and outcome evaluation toward the cesarean section were measured with 7 and 5 items, respectively. The items were rated on a 5-point scale ranging from 1 (strongly disagree) to 5 (strongly agree). Higher scores display a more positive attitude to the cesarean section. Normative beliefs were assessed concerning other important. In the present study, normative beliefs toward the cesarean section were measured with six items. The items were rated on a 5-point scale ranging from 1 (strongly disagree) to 5 (strongly agree). Motivation to comply with each of the referent groups was measured with items for each group. In the present study, the motivation to comply with the cesarean section was measured with three items. The items were rated on a 5-point scale ranging from 1 (strongly disagree) to 5 (strongly agree). Higher scores indicate more subjective norms persuasive to the cesarean section. The intention to use was assessed using three items. The items were rated on a 5-point scale ranging from 1 (very unlikely) to 5 (very likely). Higher scores indicate the intention to cesarean section more frequently.
Ethics
The ethics committee of Mazandaran University of Medical Sciences approved the study. All pregnant participants gave their written informed consent.