en بهداشت Health تحقیقی Original article <div style="text-align: justify;"><span style="font-size:12px;"><span style="font-family:Times New Roman;"><b>Background:</b> The validity and reliability of measurement instruments are fundamental prerequisites for high-quality research. This study aimed to develop and evaluate the psychometric properties of a newly designed instrument to assess maternal breastfeeding behavior based on the Theory of Planned Behavior (TPB).<br> <b>Methods:</b> This cross-sectional study involved the development of an initial 51-item questionnaire derived from a comprehensive literature review of databases including SID, Magiran, PubMed, Scopus, and ScienceDirect. Face and content validity were assessed qualitatively through expert panel review and quantitatively using the Content Validity Ratio (CVR) and Content Validity Index (CVI). Construct validity was examined using exploratory factor analysis (EFA) and confirmatory factor analysis (CFA). Reliability was evaluated using Cronbach&rsquo;s alpha and the intraclass correlation coefficient (ICC).<br> <b>Results:</b> Quantitative content validity indices were acceptable (CVR = 0.62, CVI = 0.79). Exploratory factor analysis identified a six-factor structure &mdash; attitude, subjective norm, perceived behavioral control, self-efficacy, intention, and behavior &mdash; accounting for 62% of the total variance. The Kaiser-Meyer-Olkin measure of sampling adequacy was 0.82. Confirmatory factor analysis supported the factor structure and demonstrated good model fit (&chi;&sup2;/df = 1.18, RMSEA = 0.052, CFI = 0.939, GFI = 0.93, AGFI = 0.91). The instrument also exhibited strong reliability, with ICC values ranging from 0.80 to 0.92 and Cronbach&rsquo;s alpha coefficients between 0.80 and 0.93 across all constructs.<br> <b>Conclusion</b>: The findings indicate that the TPB-based questionnaire is a valid and reliable instrument for assessing maternal breastfeeding behavior and is suitable for use in future research and clinical practice.</span></span></div> Behavior Control, Psychometrics, Self-Efficacy, Theory of Planned Behavior 43 49 http://goums.ac.ir/jorjanijournal/browse.php?a_code=A-10-115-5&slc_lang=en&sid=1 Seyed Kamal Mirkarimi ak.mirkarimi@gmail.com 100319475328460010520 100319475328460010520 No Health Management and Social Development Research Center, Golestan University of Medical Sciences, Gorgan, Iran Maryam Maghsoudlou maryam.maghsoodlo@gmail.com 100319475328460010521 100319475328460010521 Yes Department of Nursing, Amol School of Nursing and Midwifery, Mazandaran University of Medical Sciences, Sari, Iran Nazanin Tahernejad Nazanin.taheri76@gmail.com 100319475328460010522 0009-0009-5738-6569 No International Campus, Golestan University of Medical Sciences, Gorgan, Iran