For the record, and to be completely accurate, the study had 95 participants. (Or as it's also known in academic circles, "a whopping 95 participants.") However, Secretary Clinton is correct that it did use 21 undecided voters. And is correct that the study -- which was not published in a peer-reviewed publication -- has been debunked.
It should also be noted that yesterday Politifact asked Dr. Epstein if he took issue with Trump's assertion about his study. He answered -- "I sure do. I have never said that Google deliberately manipulated the 2016 election."