I found this on another website, not sure if it helps.
DOG FOOD RATINGS SCALE AND CRITERIA
Start with a grade of 100
•- For every listing of “by-productâ€, subtract 10 points.
•- For every non-specific animal source (“meat or “poultryâ€, meat meal or fat) reference, subtract 10 points.
•- If the food contains BHA, BHT or ethoxyquin, subtract 10 points. (these are known cancer causing agents.)
•- For every grain “mill run†or non-specific grain source subtract 5 points.
•- If the same grain ingredient is used two or more times in the first five ingredients (i.e. “ground brown riceâ€, brewer’s riceâ€, “rice flourâ€, are all the same grain), subtract 5 points.
•- If the protein sources are not meat meal and there are less than two meats in the top three ingredients, subtract 3 points.
•- If it contains any artificial colorants, subtract 3 points.
•- If it contains ground corn or whole grain corn, subtract 3 points.
•- If corn is listed in the top five ingredients, subtract 2 more points.
•- If the food contains any animal fat other than fish oil, subtract 2 points.
•- If lamb is the only animal protein source (unless your dog is allergic to other protein sources), subtract 2 points.
•- If it contains soy or soybeans, subtract 2 points.
•- If it contains wheat (unless you know that your dog isn’t allergic to wheat), subtract 2 points.
•- If it contains beef (unless you know that your dog isn’t allergice to beef), subtract 1 point.
•
EXTRA CREDIT
•- If any of the meat sources are organic, add 5 points.
•- If the food is endorsed by any major breed group or nutritionist, add 5 points.
•- If the food is baked not extruded, add 5 points.
•- If the food contains probiotics, add 3 points.
•- If the food contains fruit, add 3 points.
•- If the food contains vegetables (NOT corn or other grains) add 3 points.
•- If the animal sources are hormone-free and antibiotic-free, add 2 points.
•- If the food contains barley, add 2 points.
•- If the food contains flax seed oil (not just the seeds), add 2 point.
•- If the food contains oats or oatmeal, add 1 point.
•- If the food contains sunflower oil, add 1 point.
•- For every different specific animal protein source (other than the first one, count “chicken and chicken meal†as one protein source, but “chicken†and “venison†as 2 different sources) add 1 point.
•- If it contains glucosamine and chondroitin, add 1 point.
•- If the vegetable have been tested for pesticides and are pesticide-free, add 1 point.
SCORES:
•OVER 100 = A+ SUPERB!
•94 – 100 = A BEST!
•86 – 93 = B STILL GOOD
•78 – 85 = C AVERAGE FOOD, COULD BE IMPROVED
•70 – 77 = D YOU SHOULD CONSIDER CHANGING.
•69 = F AWFUL! POTENTIALLY DANGEROUS! CHANGE IMMEDIATELY