Yep, that is due to order flow from retail investors. They always put their orders in at the open (that is why Mondays can be risky) or at the close.

You can see this by looking at the difference between the return on stocks in the first/last hour against the return over the rest of the day. I have no idea if this effect still exists today but you used to be able to print money from this (and I am sure it still works in places like China with lots of retail investors).

Either that or frantic buying at the end. Impossible to predict.

Interesting. Is that based on your experience or is there somewhere I can read more on that trend?