[O] how to include effort in agenda prefix?

[Michael Gilbert]

Hi all —

I want to be able to skim across my agenda and see effort estimates. I have 
been looking at the variable org-agenda-prefix-format and wondering if use of 
the expression evaluation option in there is the way to do it. However, while I 
have configured this prefix to suit me in other ways, writing a suitable 
expression to include the effort of the item is beyond my current skills. Any 
advice?

TIA!

— Michael