"The plural of anecdote is data."

Greyson writes: "Quoting personal experiences is not objective evidence from a scientific perspective, and many scientists are dismissive of what are characterized as anecdotal accounts." Yet, he reminds us: “Most research starts with scientists collecting, verifying, and comparing anecdotes until patterns in these stories become apparent, and then from those patterns emerge hypotheses, which can then be tested and refined. Collections of anecdotes, if they are investigated rigorously, are of immense value in medical research. They were critical, for example, in the discovery of AIDS and Lyme disease, and in discovering unexpected drug effects. As political scientist Raymond Wolfinger said a half century ago, ‘The plural of anecdote is data.’”

Greyson adds: “Some of my medical colleagues dismiss near-death experiences as pure fantasy and for that reason regard any research on near-death experiences as unscientific. But what makes an investigation scientific is not the topic being studied. What makes an investigation scientific is whether it’s based on rigorous observations, on evidence, and on sound reasoning.” For instance, Greyson argues researcher Jan Holden: “reviewed ninety-three reports of out-of-body perceptions during near-death experiences and found that 92 percent were verified by outside sources as completely accurate, while 6 percent contained some error, and only 1 percent was completely wrong.” 

In Holden's study anecdotal accounts were confirmed and thus became objective evidence.

Bruce Greyson, After: A Doctor Explores What Near-Death Experiences Reveal about Life and Beyond (2021), 45-46 .