What aspect of evidence must support an agency's final decision under APA?

A final decision made by an administrative agency under the Administrative Procedure Act (APA) must be supported by evidence that is probative and substantial. This requirement ensures that the agency's findings are grounded in sufficient facts, which enhances the legitimacy and reliability of the decision-making process.

Probative evidence is that which is relevant and material to the issues at hand, capable of proving something essential to the case. Substantial evidence means that the evidence is enough to persuade a reasonable person of the truth of the conclusions drawn from it. This standard is vital for maintaining a fair and just administrative process, as it implies that the agency's decisions are not arbitrary but are based on adequate factual backgrounds.

In contrast, minimal evidence would not satisfy this requirement, as it implies that decisions could be made based on weak or inconclusive data, undermining the integrity of the agency’s authority. Relying solely on expert testimony could limit the evidential basis too narrowly since a wide range of evidence can contribute to a more balanced and comprehensive understanding of the issues involved. Lastly, while affidavits from witnesses can be a form of evidence, they do not encompass the full range of probative and substantial evidence necessary for a final decision; thus, they alone would not suffice to meet