Final answer:
If a management accountant ignores data in favor of unsupported opinion, it would directly violate the 'credibility' portion of the IMA Code of Conduct, which calls for objective and fair communication of information.
Step-by-step explanation:
When a management accountant ignores data in favor of unsupported opinion, this action would speak most directly to the credibility part of the IMA Code of Conduct. The IMA Code of Conduct is designed to promote ethical professional practices among management accountants. Part of a management accountant's role is to provide accurate and factual information to support business decisions. Ignoring data undermines the trustworthiness of the information provided, thus affecting the credibility of the accountant's work. Credibility requires that management accountants communicate information fairly and objectively, which helps users of this information in making informed decisions. Therefore, favoring opinion over factual data would directly contravene the credibility standard of the IMA Code of Conduct.