Just because someone markets himself as an “expert witness,” is hired, and offers an opinion does not make that opinion reliable or admissible. Especially when the expert witness offers a liability opinion that offers three possibilities, but not a single probability, as occurred in a file I handled in 2017.
A customer slipped and fell on water droplets near a corn on the cob display in a grocery store. No fact witness knew how the water got there and the store had no notice of them. So the customer hired an expert witness to determine the water’s source and offer a liability opinion. He offered three theories that he considered equally plausible.
24 Q. The three subparts that you have for
25 Paragraph 7, water leaking from the display, the floor mat
1 we just discussed, and the water leaking from the shopping
2 cart, are these all equally probable?
3 A. Yes.
4 Q. Is there any way for us to distinguish one
5 from the other as being more probable?
6 A. I think the most probable one would be A,
7 which is why I put it in that order, just because the more
8 mats with water, the more likely that drainage was a problem
10 But with the limited information we have from
11 the investigation, I think this is the best I have at the
The expert’s entire factual basis for these theories was just watching the store video that had observed the area of the fall.
6 Q. Based on what you’ve seen thus far in the
7 case, are you able to tell where that water that
8 [customer] fell on originated from?
9 A. It either originated from the display itself
10 or the corn, as it said on video, or it originated from the
11 customer who is seen leaving shortly before she slips with a
12 shopping cart full of corn husks.
13 Q. How do you know it originated from one of
14 those two sources?
15 A. Just that those would be the two logical
16 places that the water would be coming from, based on what we
17 see on video for the time period before the incident.
The expert applied no scientific method to reach this opinion, he just watched the video like everyone else in the case. He admitted in his deposition that at no point on the video could he see water coming from the corn display or a cart of corn that another customer pushed away. The expert offered no definitive opinions as to the water’s source, only more speculation based upon inconclusive video. He also discounted, without explanation, why the water could not have come from any one of the 5 unidentified customers who passed through the spot where the customer fell between when the last employee cleaned the area and when the fall occurred less than six minutes later.
Would the expert’s opinions have been excluded? I hoped so, but never found out because the case resolved. The point of this post is that offering thinly support opinions about possibilities does not make a single, admissible probability.
 I use the term “expert” loosely in this context because I harbored doubts as to whether the expert was in fact an expert at anything other than marketing to lawyers, but I digress.