I actually think full-time RA roles are very commonly (probably more often than not?) publicly advertised. Some fields even have centralizedjob boards that aggregate RA roles across the discipline, and on top of that, there are a growing number of formalized predoctoralRA programs at major research universities in the U.S. I am actually currently working as an RA in an academic research group that has had roles posted on the 80,000 Hours job board. While I think it is common for students to approach professors in their academic program and request RA work, my sense is that non-students seeking full-time RA positions very rarely have success cold-emailing professors and asking if they need any help. Most professors do not have both ongoing need for an (additional) RA and the funding to hire one (whereas in the case of their own students, universities often have special funding set aside for students’ research training, and professors face an expectation that they help interested students to develop as researchers).
Separately, regarding the second bullet point, I think it is extremely common for even full-time RAs to only periodically be meaningfully useful and to spend the rest of their time working on relatively low-priority “back burner” projects. In general, my sense is that work for academic RAs often comes in waves; some weeks, your PI will hand you loads of things to do, and you’ll be working late, but some weeks, there will be very little for you to do at all. In many cases, I think RAs are hired at least to some extent for the value of having them effectively on call.
I actually think full-time RA roles are very commonly (probably more often than not?) publicly advertised. Some fields even have centralized job boards that aggregate RA roles across the discipline, and on top of that, there are a growing number of formalized predoctoral RA programs at major research universities in the U.S. I am actually currently working as an RA in an academic research group that has had roles posted on the 80,000 Hours job board. While I think it is common for students to approach professors in their academic program and request RA work, my sense is that non-students seeking full-time RA positions very rarely have success cold-emailing professors and asking if they need any help. Most professors do not have both ongoing need for an (additional) RA and the funding to hire one (whereas in the case of their own students, universities often have special funding set aside for students’ research training, and professors face an expectation that they help interested students to develop as researchers).
Separately, regarding the second bullet point, I think it is extremely common for even full-time RAs to only periodically be meaningfully useful and to spend the rest of their time working on relatively low-priority “back burner” projects. In general, my sense is that work for academic RAs often comes in waves; some weeks, your PI will hand you loads of things to do, and you’ll be working late, but some weeks, there will be very little for you to do at all. In many cases, I think RAs are hired at least to some extent for the value of having them effectively on call.