How do PhD candidates perceive good research practices in the Netherlands Code of Conduct for Research Integrity?

INTRODUCTION: Research misconduct and questionable research practices compromise the quality of scientific research. The Netherlands Code of Conduct for Research Integrity 2018 outlines five core principles and 61 standards for good research practices intended to guide researchers and research integrity committees. For the code to function, its 61 standards must be perceived as clear and relevant by those who perform the research practices. These include researchers including PhD candidates, who contribute about 40% of Dutch research full-time equivalents. This study examines how PhD candidates in the Science and Medicine faculties at Leiden University perceive these 61 standards. METHODS: A total of 332 PhD candidates (73% participation proportion) evaluated the standards in the Dutch code as part of a mandatory research integrity course at Leiden University and consented to share their responses for research purposes. Each participant rated half of the standards using Likert-type scales for clarity, relevance, frequency, and seriousness of non-adherence. In addition, open-text responses were collected and categorized according to the code's five core principles. RESULTS: Overall, 83% of clarity ratings and 77% of relevance ratings scored 4 or 5, indicating a generally positive perception of the standards. However, the perceived frequency of non-adherence varied across standards (5-34%). There were discrepancies in severity assessments, where standards that should represent minor shortcomings were perceived as serious misconduct and the other way around. Open-text responses primarily emphasized honesty and transparency, while independence was rarely mentioned, and participants also highlighted values not explicitly covered by the current code, such as equality and ethical collaboration. DISCUSSION: PhD candidates generally regarded the Dutch Code's 61 standards as clear and relevant, but their ratings of how serious non-adherence should be considered often diverged from the code's a priori three-tier severity framework. Several standards labelled as "minor shortcomings", particularly those related to ethics approvals, authorship, and transparent reporting, were frequently classified as research misconduct, while one plagiarism-related standard (practice 34) was more often seen as a questionable practice. These results suggest the need to refine currently ambiguous formulations and reconsider the a priori severity categories.