This cross-sectional methodological study was carried out in 2017–2018.
Sample
There is no universal consensus over sampling adequacy in psychometric studies. However, samples greater than 1000 are considered adequate 23. Therefore, sample sizes for exploratory and confirmatory factor analyses in the present study were considered to be 800 and 500, respectively. Sampling was purposively done from June 2017 to March 2018 in three central cities in Mazandaran province, Iran, namely Amol, Babol, and Sari. Inclusion criteria were ability to read and write in Persian, an age of more than eighteen and no history of BC among family members (i.e. mother, sister, or daughter).
Instrument
The instrument of the study was BCSBQ developed by Kwok et al. in 2010. BCSBQ has twelve items on women’s attitudes towards general health assessment, their knowledge, attitudes, and perceptions regarding BC, and their screening practice in the area of mammography. BCSBQ items are scored using a Likert-type scale from 1 (“Completely agree”) to 5 (“Completely disagree”). The total score of the questionnaire is changed into a 0–100 scale. The developers of the questionnaire found that it has three subscales and reported a Cronbach’s alpha of 0.84 for it 22
Translation
After obtaining necessary permissions for using BCSBQ from professor Kwok, the questionnaire was translated into Persian based on the forward-backward translation protocol proposed by the World Health Organization 24. Initially, a reproductive health specialist and an English expert independently translated the questionnaire into Persian and then, the authors developed a single Persian translation of BCSBQ based on their translations. After that, two other translators (a reproductive health specialist and an English expert) independently back-translated the final Persian version of the questionnaire into English. The authors used these two English translations to develop a single English translation. Finally, the final English translation was sent to professor Kwok for the purpose of approval. She approved that our English BCSBQ was similar to her original questionnaire.
Psychometric evaluation
Face validity evaluation
Twenty women were provided with the Persian BCSBQ and were asked to assess the clarity and simplicity of its items. None of them reported ambiguities in BCSBQ items.
Content validity evaluation
Content validity was evaluated through qualitative and quantitative methods 25. In qualitative content validity evaluation, the questionnaire was given to ten experts in instrument development and healthcare (six reproductive health specialists with PhD degree, one health education specialist with master’s degree, two midwives with master’s degree, and one clinical psychologist with PhD degree). . Qualitative content validity of the questionnaire was approved after making revisions recommended by the specialists. They were asked to evaluate appropriate wording and placement of the items. They recommended some linguistic amendments to the questionnaire items. Quantitative content validity evaluation was performed through calculating content validity ratio (CVR) and content validity index (CVI) for the questionnaire. For CVR calculation, the aforementioned ten specialists rated the essentiality of BCSBQ items as “Essential” (scored 1), “Not essential, but useful” (scored 2), and “Not essential” (scored 3). Items which were considered essential by nine specialists were kept. Among ten specialists, nine determined that all items were essential and therefore, no item was removed. For CVI calculation, the specialists were asked to rate the relevance of the items on the following scale: 1: “Irrelevant”; 2: “Somewhat relevant”; 3: “Acceptably relevant”; 4: “Completely relevant”. Subsequently, CVI of each item was calculated through dividing the number of specialists who had rated that item 3 or 4 by ten. CVI values of 0.78 and more were considered acceptable 26Moreover, quantitative content validity evaluation showed that all items had CVRs greater than 0.8 and CVIs greater than 0.78. Therefore, none of the items were removed.
Construct validity evaluation
Construct validity was evaluated through with exploratory and confirmatory factor analysis. Exploratory factor analysis (EFA) is a multivariate statistical technique that describer the relationship of some observed variables by a relatively number of factors 27 Initially, maximum likelihood EFA with varimax rotation was performed. Kaiser-Meyer-Olkin (KMO) test was run to determine sample adequacy, while Bartlett’s test was run to evaluate homogeneity of variance. Then, latent factors were extracted based on Horn’s Parallel Analysis, and scree plot28. According to the three-indicator rule, each factor had to have at least three items. All these analyses were performed in SPSS25, SPSS R-Menu2 JASP0.9.0.1. After EFA, confirmatory factor analysis (CFA) with maximum likelihood estimation was performed using the AMOS24 software to test the fit of the extracted model based on the most commonly used indices for model fit. CFA state the degree of disharmony, between predicted and empirical factor structure in χ2 and indices29 . These indices were Parsimonious Comparative Fit Index (PCFI), Parsimonious Normed Fit Index (PNFI), Minimum Discrepancy Function divided by Degrees of Freedom (CMIN/DF), Root Mean Square Error of Approximation (RMSEA), Adjusted Goodness of Fit Index (AGFI), and Comparative Fit Index (CFI).
Convergent and discriminant validity evaluation
Based on Fornell and Larcker’s criteria 30, convergent and discriminant validity and construct reliability were evaluated through calculating Average Variance Extracted (AVE), Maximum Shared Squared Variance (MSV), Average Shared Squared Variance (ASV), and Composite Reliability (CR). In order to confirm convergent validity, AVE should be greater than 0.5 and CR should be greater than AVE. On the other hand, to ensure discriminant validity, AVE should be greater than MSV 31. Moreover, a scale has acceptable convergent validity when all its items are close together and share a large amount of variance, while it has acceptable discriminant validity when the extracted factors are completely independent from each other32. Convergent and discriminant validity evaluations revealed that all factors had acceptable convergent and discriminant validity.
Relative reliability evaluation
Relative reliability was evaluated through the test-retest method, in which twelve participants filled out BCSBQ twice with a two-week period in between. Then, intraclass correlation coefficient (ICC) was calculated using two-way mixed effects model. Moreover, Cronbach’s alpha, McDonald’s omega, and Average inter-item correlation were calculated for internal consistency evaluation 31. Internal consistency assesses item homogeneity, or the degree to which the items on a test jointly measure the same construct 33. Then, construct reliability (CR) was evaluated. CR value greater than 0.7 was considered as acceptable reliability34.
Absolute reliability evaluation
ICC provides no accurate information about the accuracy of the scores. Therefore, absolute reliability was estimated by calculating standard error of measurement (SEM) using the following formula, (37).
Ethics consideration
This study is approved by the Ethics Committee of Health Research Institute in Babol University of Medical Sciences. [Grant number: MUBABOL, HRI.REC.1396.10].