"Rater A person involved with clinical research who administers a scale to a research participant".
"The principle investigator and/or a designated sub-investigator who is certified to rate the scale in the study should co-rate the study subjects with the rater(s) in training, until such time as the investigator certifies, in writing, that the rater is competent to administer the scale(s) on his or her own."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4301026/

"the investigator is the responsible leader of the team. 'Subinvestigator' includes any other individual member of that team."
http://www.appliedclinicaltrialsonline.com/investigators-and...

"Huvudprövare (eng. principal investigator ). Den prövare som är huvudansvarig för prövnings genomförande på en klinik."
"Medprövare (eng. sub-investigator). Övriga läkare/tandläkare som arbetar med prövningen på en klinik."
https://old.liu.se/medfak/forumostergotland/kurser-utbildnin...

"Ofta finns det en ansvarig prövare och en eller flera medprövare i en klinisk prövning."
https://www.sahlgrenska.se/omraden/omrade-5/onkologi/forskni...