When teaching research methodology, it is crucial that examinations be examples of correct instrument creation and validation. With this objective in mind, an exploratory level instrument validation design study was conducted to construct a documentary questionnaire to assess knowledge on the topic of population, sample, and sampling as part of the university course of Scientific Research Methodology. The study was divided into two phases. In the first phase, a questionnaire was created, and its content validity was determined. In the second phase, the questionnaire was validated using various metrics, including construct and criterion validity, reliability, stability, and performance. To assess construct validity, Principal Component Exploratory Factor Analysis with rotated solution by the VARIMAX method was used, using SPSS software (27.0). Confirmatory Factor Analysis was conducted using IBM SPSS AMOS. As a result, a questionnaire was obtained that accurately measures knowledge on the subject of population, sample, and sampling, pertaining to the subject of Methodology of Scientific Research. The questionnaire has adequate content, construct, and criterion validity, as well as appropriate reliability, stability, and performance.