What's the shiny rate for Psyduck this weekend?

No shiny of any kind for me since Feebas day,

As with most shinies, it's a spectrum where some people get lots (I have friends who have gotten over 10 so far) while others get shut out completely. I'm in the latter camp, as I have been for Taillow and Zigzagoon. And Feebas (but most seem to have lost out on that one). And Delibird. And Drowzee. And Nidoran....

Trying to figure it out will give you a headache.

It appears to be the same as the other Safari Zone events in my local groups. 1/50ish?

Seems to be better odds than normal shinies but lower than community day. Could be the same boost that Roselia/Plusle/Minun/Wingull/Pinsir got.

45 is virtually nothing.

45 is absolutely nothing and only noobs and casuals shiny check.... catching is what makes a player strong