Stars from assistant

how is the assistant giving stars? where is it based on?
is it based on the CA/PA comparing to the prognosed place in the league?

My given stars from the assistant switch a lot during a season.. upwards and downwards.

It's all relative to your own team iirc. Some people go way overboard in judging players by stars, playing a player with a better star rating than another player, despite the second player having better attributes. I only tend to bother looking at the stars for their future progression.