Opinion evidence should always be based upon what type of information?

Opinion evidence is grounded in facts, as it provides a basis from which an individual's interpretation or conclusion is drawn. In legal contexts, it is essential that opinions, particularly those presented in court or during investigations, are supported by factual information rather than just personal beliefs or unverified assertions. This ensures that the opinion has credibility and relevance to the case at hand.

Research studies might inform an expert's opinion, but they do not constitute the essence of opinion evidence itself, which must be anchored in observable facts. While opinions themselves are inherent to the answer choices, they need to be substantiated by factual information to hold weight in legal proceedings. Speculation, on the other hand, lacks the foundation of solid evidence and can lead to unreliable conclusions, making it an unsuitable basis for opinion evidence. Thus, the emphasis on facts reinforces the integrity and validity of the opinions expressed in a criminal investigation context.