Developing the 'Imagery during exercise questionnaire-Gym Version' and assessing its content validity

Mental imagery (MI) is a psychological technique traditionally applied outside exercise contexts. However, recent studies indicate its potential benefits during physical activity, particularly for enhancing positive emotions and self-regulation of exercise behavior. While existing questionnaires capture aspects of MI regarding the exercise, none are specifically designed to evaluate MI during training. Therefore, it is necessary to create a new questionnaire. Establishing its content validity (CV) is the initial step in this process. Despite its importance for subsequent validity assessments and the reliability of the measurement instrument, CV is often overlooked or superficially addressed, possibly owing to a lack of comprehensive guidelines. In response to these needs, the aim of this study was to develop the "Imagery during Exercise Questionnaire-Gym Version" (IdEQ-GV) to assess the functions of MI during exercise and to measure its CV. This study also provides a step-by-step presentation of the content validation process. The development of the IdEQ-GV involved instrument design and judgmental evidence from academic experts and lay experts (i.e., potential research subjects). The first version of the questionnaire, consisting of 34 items across 6 dimensions, was assessed by three content experts who evaluated its CV in terms of relevance, essentiality, clarity, and comprehensiveness and provided feedback. The second version, comprising 28 items across 5 dimensions, was re-evaluated by content experts and discussed in cognitive interviews with 13 gym members, who also provided feedback and scores regarding comprehensibility and comprehensiveness. After making the necessary modifications, the third version of the IdEQ-GV, containing 24 items, was evaluated by a new sample of 20 exercisers for comprehensibility. The methods used to quantify CV included the content validity index (CVI), the scale-level CVI (S-CVI), which comprises the average CVI (S-CVI/Ave) and universal agreement (UA) among experts (S-CVI/UA), and the content validity ratio (CVR). The IdEQ-GV was found to have an excellent CV regarding relevance, with an S-CVI/UA of 1.00. For clarity, the S-CVI/Ave was 0.95. For essentiality, the average CVR of the scale was 0.83. For comprehensiveness, according to the content experts' scores, the S-CVI/Ave was 0.93, while the first sample of exercisers gave it a perfect score. Regarding comprehensibility, the final sample of exercisers rated the SCVI/