Looking for some helpful suggestions. I took different positive and negative factors to assess the habitat quality of my study sites. Four of these factors were positive, while four were negative. Each of these factors were assigned a value from 1 to 5 for both negative positive factors (5 reflective of the most desirable score and vice versa). This score was then assigned a weightage which was specific for each factor. E.g. The first positive factor score was multiplied with 4, the second factor score multiplied by 3, the third factor's score by 2, and the fourth positive factor's score by 1. Similar things were done for the negative factors. At the end i added up all positive factors' score (X), and all negative factor scores(Y). However, now when i am supposed to calculate final habitat/site criteria based on these positive and negative factors, i am very much confused, I don't know if i should sum up X and Y, or if should take their difference (X-Y). if i take a difference, a certain site's total score becomes negative. Addition does give me feasible results. But I am not sure if the positive and negative factors should be summed up or subtracted.

Note: I wish to see how different positive and negative factors affect overall habitat quality but Iam afraid summing up will not show the detrimental effect of negative factors o habitat, and on the other hand subtraction keeps resulting in negative values for some sites.

I hope my question is understandable.