The scoring rubric.
Every comparison on VitFacts uses the same scoring model. If you can replicate our math and arrive at the same ranking, we are doing our job right.
Step 1 — Form scoring
For each active ingredient, we score every form on the same five axes.
| Axis | What we measure | Source |
|---|---|---|
| Absorption | % of dose reaching bloodstream | NIH ODS, primary pharmacokinetic studies |
| Active dose | mg of usable active per label mg | Calculated |
| Half-life | hours in bloodstream | Primary pharmacokinetic studies |
| Side effects | GI tolerance, drug interactions | NIH ODS, Cochrane |
| Best use case | clinical indication, population | Examine.com, NIH ODS |
Step 2 — Per-effective-dose math
Once forms are ranked, we compute per-effective-dose price for every product.
Per-effective-mg = (Product price ÷ Servings per bottle) ÷ (mg per serving × absorption %)
Worked example — Vitamin C
Product A: 60 capsules × 1000 mg ascorbic acid @ $20
- Servings per bottle = 60 · Price per serving = $20/60 = $0.33
- Active dose = 1000 mg × 0.90 (absorption) = 900 mg
- Per-effective-mg = $0.33 / 900 = $0.0004 / mg
Product B: 30 capsules × 500 mg liposomal vitamin C @ $35
- Servings per bottle = 30 · Price per serving = $35/30 = $1.17
- Active dose = 500 mg × 0.95 (liposomal absorption) = 475 mg
- Per-effective-mg = $1.17 / 475 = $0.0025 / mg
Product A (ascorbic acid, 1000 mg) is 6× cheaper per effective mg despite the smaller label. That is the metric we report.
Step 3 — Citation hierarchy
We cite in this order of preference. Brand marketing claims are not used as evidence for clinical claims.
- Primary sources — ISSN-indexed journal articles, NIH ODS fact sheets, Cochrane systematic reviews.
- Independent reviewers — Examine.com evidence summaries (with underlying study links).
- Product-specific data — Certificate of Analysis (CoA) from the brand, retailer product photos, product label.
- Tell us if we missed something — see contact.
Step 4 — Price snapshots
Prices are checked weekly. Every figure is tagged with the date of capture and the retailer URL.
- If a price cannot be verified, the cell reads
[price unavailable]— never invented. - TH-availability claims are cross-checked with each brand's official Thai store + Chemist Warehouse / Lazada / Shopee.
- AU-availability defaults to Chemist Warehouse AU + the brand's official AU site.
What we don't do
- We do not accept compensation for coverage, placement, or ranking.
- We do not display weight-loss, "detox," or patent-medicine claims.
- We do not recommend products to specific people — we present the evidence and let you choose.
- We do not cite brand websites as primary evidence for clinical claims about the brand's own products.