If you’ve ever been on a jury panel, you know that there are two types of witnesses: fact witnesses and expert witnesses. There are different requirements for each role, and they serve different purposes, though the ultimate purpose, of course, is to get to the truth of the matter.

Fact witnesses are those individuals who have personal knowledge about a particular matter. They have personally experienced or observed something and are competent to testify about it —truthfully. But they are not qualified or permitted to testify to things beyond their personal knowledge. That will draw an objection of “speculation.”

Expert witnesses are not expected to have personal knowledge of the matter at hand. Instead, they have a particular expertise that is relevant to the case. They are permitted to testify about standard procedures and what they would expect to see, now and in the future, based upon their knowledge and experience of similar cases or events. Before they can say a word about the case, however, there are specific requirements to establish them as an expert and permit their testimony. This includes things like education (degrees from reputable schools, or specialized training, for example), experience (how familiar are they with these types of cases, how many similar cases have they worked on/examined, etc.), what the professional literature says, and whether that education and experience makes them more knowledgeable about a matter than the average person.

When an expert testifies, he or she must explain the basis of their opinion, the process by which they came to that conclusion, and cite to any relevant studies, data, etc.

Both witnesses, the fact witness and the expert witness, must testify only to things that are admissible under the rules of evidence. For example, the fact witness cannot testify as to what other people saw or heard, as that will likely draw a hearsay exception. They cannot, generally speaking, make predictions about other situations, because they don’t have the expertise to make those predictions based upon one experience that they had.

Because I’m a lawyer, I tend to view the social media posts around COVID19 in this same light.

If you have had the virus, you are a “factual witness” who can “testify” to your experience. If someone near you has had it, you can testify as to what you observed (e.g., “her breathing was labored”), but probably not opine about that person’s experience with the virus (e.g., “I’m sure it felt like breathing glass”). You also are probably not qualified to predict how many people might get it, or what their experiences are going to be.

Infectious disease specialists and epidemiologists are the “expert witnesses” who cannot “testify” as to what your experience was, but rather to the broader information and implications. They are the ones that have the training and experience to do crunch the numbers, to know what data is relevant and what isn’t, and to compare and contrast a particular virus to other viruses.

If you share a post that poses as an “expert witness,” but starts out, “My friend’s sister is a nurse and she said…” I’m probably not going to read that (unless I know you and the friend, and the nurse and trust what she has to say).

If your post starts out, “I created my own spreadsheet and here is what is going to happen…” without telling me who you are, why you are qualified to make those predictions, and the data upon which you relied (with citations), I’m probably not going to pay any attention to it.

If you cite CNN, FOX, MSNBC, or any other news organizations, I am not going to rely on that, either, unless they tell me who they received that information from, where the data came from, and I can confirm that the statement is accurate and not taken out of context.

If, on the other hand, I see a post written by someone who has the expertise to speak on the matter, cites to their (reliable) sources, and shows me the data, I will definitely listen. If they tell me things like, “original predictions were X, but now that we have more data from the U.S. (which is a different situation than China or Italy because of Y), we have revised our predictions to Z” I will also pay attention, because they are telling me not only what is different about their prediction, but why it is different (again, with evidence to support their position).

Trials often have competing “experts,” again, similar to the COVID-19 situation. Like jurors, we need to objectively weigh the evidence presented by both sides to determine which is more reliable, and which makes more sense. It is true that some jurors are “excused” from serving due to real or potential biases. But because we are not “excusing” anyone from participating in the conversation around COVID-19, we have to be particularly careful about setting aside bias, and even what we think we know based upon our own, limited experiences.

As Dan Heath says in his book, Upstream, “Data takes you away from philosophical insights. You move away from anecdotal fights about what people think is happening to what is happening.”[1]

When you read a post about COVID-19, especially one that seems particularly alarming, ask yourself:

  1. Who is the person making the statement? What “credentials” do they have to suggest I should trust what they are telling me?
  2. Where did they get their data? Have they provided citations so I can see the original source, and confirm that it says what the author tells me it says?
  3. Does the statement appear to be objective and factual, or is it full of adjectives designed to create an emotional response? In other words, does it encourage me to think, or feel?
  4. Does the evidence support what they are telling me?
  5. Are there qualifiers that would change their “prediction,” and do those qualifiers exist (e.g., when they start out “Absent any steps taken to…” and I know there have been steps taken, how should I interpret the data they have presented with the “Absent any steps taken” presumption?

Let’s be smart about this. Let’s make sure we aren’t letting our fears drive our decisions. Let’s make sure that the things we are reading are trustworthy. That doesn’t mean predictions and recommendations won’t change; they likely will change, because this is a new virus. But the trusted sources’ predictions and recommendations will change with new and good data.


[1] Heath, D. (2020). Upstream: the quest to solve problems before they happen. New York: Avid Reader Press., citing a 2018 interview with Beth Sandor, head of Built for Zero, a national effort to help communities end homelessness.

Fact Witnesses, Expert Witnesses, and COVID-19
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