PSI+ Scoring Methodology
Every product in our database receives a PSI+ score from 0 to 100, translated into a letter grade from A+ to F. This page explains exactly how we calculate scores, where our data comes from, and our commitment to editorial independence.
What is PSI+?
PSI+ (Pet Supplement Index Plus) is our proprietary scoring system that evaluates pet supplements across four evidence-based dimensions. Unlike simple star ratings, PSI+ analyzes the actual formulation quality, ingredient doses, label transparency, and formula diversity to give pet owners a clear, science-backed picture of product quality.
The Four Scoring Dimensions
Ingredient Adequacy
Weight: 35%Are key ingredients present at clinically effective doses based on veterinary research?
How we measure: We compare each ingredient's listed amount against peer-reviewed effective dose ranges from veterinary studies. Products receive higher scores when key ingredients meet or exceed clinically validated thresholds.
Formula Completeness
Weight: 25%Does the product include all expected ingredients for its supplement category?
How we measure: We define expected ingredient profiles for each supplement category based on veterinary research. Products are scored on how many of these expected ingredients are present in their formula.
Label Transparency
Weight: 20%Are individual ingredient amounts clearly disclosed without proprietary blends?
How we measure: We evaluate whether individual ingredient amounts are clearly disclosed. Products using proprietary blends or hiding individual doses receive lower scores. Full disclosure of every ingredient amount earns maximum points.
Ingredient Diversity
Weight: 20%Does the formula include a breadth of beneficial compounds from multiple pathways?
How we measure: We assess whether the formula includes ingredients working through multiple biological pathways. A joint supplement with glucosamine, omega-3s, and anti-inflammatory herbs scores higher than one with only glucosamine variants.
Grade Scale
| Grade | Score Range | Interpretation |
|---|---|---|
| A+ | 97–100 | Exceptional — best-in-class formulation |
| A | 93–96 | Excellent — highly effective formula |
| A- | 90–92 | Very Good — strong across all dimensions |
| B+ | 87–89 | Good — above average quality |
| B | 83–86 | Above Average — solid formulation |
| B- | 80–82 | Decent — meets basic quality standards |
| C+ | 77–79 | Fair — some notable gaps |
| C | 73–76 | Average — room for improvement |
| C- | 70–72 | Below Average — multiple weaknesses |
| D+ | 67–69 | Poor — significant concerns |
| D | 63–66 | Very Poor — major formulation issues |
| D- | 60–62 | Failing — minimal effective value |
| F | 0–59 | Failing — not recommended |
Data Sources
Marketplace Scraping
Product data, pricing, and reviews from Amazon, Walmart, iHerb, and Chewy via structured API scraping.
NASC Quality Seal
Brand verification status from the National Animal Supplement Council's member directory.
PubMed Veterinary Studies
Effective dose ranges and evidence grades sourced from peer-reviewed veterinary research.
openFDA API
Animal & Veterinary adverse event reports for ingredient safety signal monitoring.
Editorial Independence Statement
PetSupplementsIndex.com operates with complete editorial independence. Our PSI+ scores are calculated algorithmically based on objective product data and are never influenced by brand relationships, advertising, or affiliate partnerships.
- •We do not accept payment from brands to alter scores or rankings.
- •All scoring criteria are publicly documented on this page.
- •Our data pipeline is automated and applies the same standards to every product.
- •Affiliate links, when present, never influence product placement or scores.