Suppose that in an academic writing we want to write about an experiment which was done in the past. In that experiment we recognized that there is an advantageous correlation between some variables. Since the experiment was done in the past, I think I should use the past tense in the main clause ("There was an advantageous ..." ). But when I want to explain what this advantageous correlation is, what tense should I use?
There was an advantageous correlation between these variables which is/was that the variables with positive value have/had bigger magnitudemagnitudes than variables with negative value.