Which of the following is NOT a type of supporting material for a speech?

Supporting materials are essential components of a speech as they provide the evidence and context necessary to bolster the speaker's main points. Statistics are utilized to present numerical data that adds credibility and persuasiveness to arguments. Testimony from experts or witnesses lends authority and can effectively illustrate a point through first-hand accounts. Anecdotes, or personal stories, can engage the audience emotionally and help to clarify abstract concepts.

In contrast, personal opinions without evidence do not qualify as supporting materials in a formal sense. They may lack the necessary backing to persuade an audience, as they are based solely on the speaker's perspective rather than objective data or verified sources. Thus, they do not enhance the speech in the same way that statistics, testimony, or anecdotes do, which is why this is the correct answer.