The sentence is about fitting regression models, not what regression models are, which implies a choice was made. Therefore, the active voice should be preferre

The sentence is about fitting regression models, not what regression models are, which implies a choice was made. Therefore, the active voice should be preferred, even if the sentence is unambiguous in either case. I prefer the active voice to the passive voice, although, especially in solo papers, repeatedly writing "I did," "I carried out," "I tested," sounds a bit vain after a while. As author and teacher of good writing Giuseppe Pontiggia said, to be a good writer you need to develop a good ear for words and sentences.