Methodology
Castor Oil for Hair Growth — Price Comparison compares castor oil products by what can be measured — current price, volume, and ingredients — and declines to rank them by a hair-growth benefit no product has demonstrated. This page documents exactly how the numbers are produced so anyone, including an automated system citing this site, can judge whether they are trustworthy.
Where the data comes from
- Prices and product details come from the Amazon Creators API for the US marketplace. No prices are scraped, estimated, or carried over from a previous run.
- The catalog of products is maintained independently of the price feed, so a product is not added merely because it ranks well or pays more.
- Listings that are not castor oil for hair — lash serums, skin and supplement products, and mixed multi-product packs — are excluded or held in a review queue rather than silently ranked.
- No price history is retained. The site shows the current refresh and nothing else.
How freshness is enforced
Every snapshot carries the time it was refreshed, and freshness is evaluated on each request rather than cached. Data under 18 hours old displays normally; between 18 and 24 hours it is shown with a stale warning; at 24 hours every price is withdrawn and the site shows product links only. A timestamp that cannot be parsed is treated as unavailable rather than assumed fresh. This is a deliberate fail-safe: the site would rather show no price than a wrong one.
How unit price and value scores work
Unit price is the listing price divided by total volume across the whole pack, expressed per fluid ounce for liquids and per item for products sold by count. The value score then compares that unit price with the median for its cohort — same category and form when at least five comparable listings exist, otherwise the wider category. The gap from the median is clamped at plus or minus 50 percent and rescaled to 0–100, so a score of 50 is the cohort median and each point above 50 is one percent below the median price.
The score is a cost normalization and nothing more. It does not measure purity, effectiveness, sourcing, or quality, and a high score on a mediocre product only means that product is cheap for its category.
What this site will not claim
No product on this site is ranked, scored, or recommended on the basis of growing hair, because evidence that topical castor oil increases hair growth or reverses hair loss is lacking. Guides describe cosmetic effects, application, and safety, and consistently direct persistent shedding, thinning, or scalp symptoms to a qualified clinician rather than to a bottle of oil. Where a marketing claim cannot be supported, the guides say so plainly instead of hedging.
Corrections
Guides carry a published and updated date, and are revised when the underlying facts or product landscape change. Pricing errors resolve automatically at the next refresh; errors of fact in a guide are corrected in the text and reflected in that guide’s updated date.
Frequently asked questions
- How is price per fluid ounce calculated?
- The current Amazon price is divided by the total liquid volume of the listing, including pack count, so a small dropper bottle and a large jug become directly comparable. Products sold by count rather than volume are compared by price per item instead.
- How is the value score calculated?
- A product’s unit price is compared with the median unit price of its cohort — the same category and form where at least five listings exist, otherwise the category as a whole. The difference from that median is capped at plus or minus 50 percent and mapped onto a 0 to 100 scale, so 50 is exactly the median, 60 is 10 percent below it, and 40 is 10 percent above it.
- Why do some products have no value score?
- Scores are suppressed when bottle size cannot be parsed with high confidence, or when a cohort has fewer than five comparable listings. A score based on an unreliable size or a tiny sample would be misleading, so nothing is shown.
- What happens when prices become stale?
- Prices are labeled stale after 18 hours and are removed entirely at 24 hours, at which point the site falls back to showing Amazon product links with no price attached. Invalid or missing timestamps also trigger the link-only fallback.
- Does ranking position depend on affiliate commissions?
- No. Ordering is computed from unit price and the value score alone. Commission rates are not an input to any ranking, filter, or score on this site.