i think i can answer your question. i dont know what propensity means but from the rest of the question, i think it means something like frequency

so, yes. each state has its own guidelines that are followed regarding both timeliness of investigation and removal policy. it is also subjective because it is based on the workers assessment of harm.

calls that come into CPS are triaged and investigated according to the level of immediate danger that is assessed. you could actually probably find the protocol for your state on-line now.

in addition, california has limited foster homes for the number of kids. for example, there are foster kids living in run-down hotels because there are not enough placements for them. other kids are put into shelters.
this has an impact as well. no placements, what do you do with the kids?

but, also, remember if other options are available, such as removing the offending parent or placing the kid in kinship care, CPS will do that.

statistically, about 50-60% of foster kids taken by CPS are RETURNED to their bioparents.
there are laws about timelines and how quickly parents rights can be terminated and how quickly parents have to work their case plans.
TPR does not happen "overnight", unless there is substantiated specific severe abuse proven or complete abandonment. by law in most states the process of TPR begins after a child is in care for 15 of 22-24 consequective months. (unless there is severe substantiated abuse or abandonment)
during this time, the parents are given multiple opportunities and support to work their case plans.

if parents dont work their plans or make progress or TPR is quick because of the above reasons,
then...
---about 15-20% of kids are adopted by other people.
---about 5-10% are adopted by other family members (grandparents, aunts, etc)
---the rest of the kids are long term foster kids. (a small percentage might have a legal guardian relationship)