The pollster is Public Policy Polling, and they spoke with 1,056 registered voters. See the last paragraph at this link:
https://www.publicpolicypolling.com/polls/a-happy-valentines-day-for-joe-biden/
On a less serious note PPP once again tested whether people think Michael Jordan or LeBron James is the greatest basketball player of all time in the wake of James breaking the all time scoring record last week. And despite that record it’s still not competitive- Jordan wins out 58-15. It was 77-14 in 2015 so James’ success over the last eight years has led to a little more ambiguity on the question but MJ still has the clear advantage.