"Children aged 5, 6, and 7 remembered 60% or more of the early-life events. In contrast, children aged 8 and 9 years remembered fewer than 40% of the early-life events".
It is wrong to disbelieve him without knowing the standard deviation of the results. 40% is an average! For all we know (I can't check, as I don't have access to the original paper), there could have been two kids who had 90% recall and eight kids who had less than 40% recall. Knowing the standard deviation (and the nature of the distribution of results, whether it's a bell curve or whatever), would allow us to determine the probability of somebody having 90% recall post-childhood amnesia. Even if that probability was only 1/100, considering more than 100 people frequent this site it's expected that a few of them would have said 90% recall.
Even if the deviation were zero, 40% recall (or 20%, or 2%) of early-life events is more than enough to remember one thing. It's very definitely wrong for someone to take the position attributed to the history professor, "that this is impossible, because children can't remember anything before the age of 3". To the contrary, we know that they can.
It is wrong to disbelieve him without knowing the standard deviation of the results. 40% is an average! For all we know (I can't check, as I don't have access to the original paper), there could have been two kids who had 90% recall and eight kids who had less than 40% recall. Knowing the standard deviation (and the nature of the distribution of results, whether it's a bell curve or whatever), would allow us to determine the probability of somebody having 90% recall post-childhood amnesia. Even if that probability was only 1/100, considering more than 100 people frequent this site it's expected that a few of them would have said 90% recall.