for what is my understanding (I'm not an expert), Norton's analyses concern about Relative Density (RD), Relative Frequency (RF) and Absolute Frequency (AF) and Prominence value (PV). They were published in a book by Norton ("Ecology of Plant-Parasitic Nematodes") in 1978. Sadly, I didn't find the original book, but I found a paper where Norton's formula were used (you can also ask the authors on RG if it was what you were searching):
Article Community analysis of soil nematodes in vegetable growing ar...