Outsourcing is rapidly increasing in the cosmetic industry. When cosmetic manufacturing activities are outsourced, product quality control and assurance procedures are important to guarantee the safety of the final products. One method to ensure the compliance of potential contract manufacturers with Good Manufacturing Practices (GMP) is auditing. Auditing can be confirmed by using GMP questionnaires. The current study aims to develop an effective instrument, in the form of a questionnaire, and to validate its content using the Delphi method. A modified Delphi method used an expert panel to develop a questionnaire-based audit preparation instrument. In the Delphi questionnaire round, 50 experts from cosmeceutical industries, relevant authorities, and universities assessed the content validity of the audit preparation instrument. The Delphi questionnaire round targeted 70 experts from the cosmetics industry; 50 completed the questionnaire, giving a response rate of 71.4%. Their agreement level on the quality of the instrument items ranged between 56 and 96%. Of the 52 items, 47 (90.4%) met the predefined criterion for an agreement rate of at least 75%. The proposed audit preparation instrument demonstrated good content validity, and the expert panel participating in the Delphi questionnaire round made a few minor suggestions for modifications. The modified Delphi method used for the content validation of the instrument proved to be suitable. However, based on the panel's feedback, additional research is needed to ensure the maximum applicability and practicality of the instrument.
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