Methodology · retail-v3-mainstream
How the DDR5 retail index works
A transparent, mainstream current-product basket is more useful than a large opaque one. These rules define what enters each weekly point, what stays out, and how the basket is kept relevant as products change.
1. Two capacity anchors
The index follows 32GB (2×16GB) and 64GB (2×32GB) desktop UDIMM kits. Both capacities are common enough to support multiple brands and large enough that tiny low-capacity products do not dominate the price-per-GB signal.
2. Product eligibility
| Rule | Included | Excluded |
|---|---|---|
| Brand universe | Kingston, Corsair, G.Skill, TEAMGROUP | Every other brand, regardless of apparent bargain price |
| Product family | One representative per memory family and capacity | RGB, colour, and closely related cosmetic variants counted as separate observations |
| Market evidence | Rating ≥4.2 and either ≥25 ratings or ≥50 bought in the past month | Missing/low ratings and thin demand evidence |
| Fulfilment evidence | Prime, meaningful recent purchase activity, or an explicit in-stock signal | A returned price with none of those availability signals |
| Stock depth | Available with no explicit thin-stock warning | Out of stock or “only 10 left” and below |
| Compatibility | Normal platform/profile qualifications | Explicit “not compatible,” discontinued, or end-of-life warnings |
| Generation | Explicit DDR5 | DDR4, DDR3, ambiguous titles |
| Form factor | Desktop UDIMM / 288-pin | Laptop SODIMM / 262-pin |
| Class | Mainstream unbuffered desktop kit | ECC, RDIMM, LRDIMM, server or workstation memory |
| Condition | New | Used, renewed, refurbished, open-box |
| Capacity | 32GB or 64GB total, two modules | Single modules, four-module kits, ambiguous totals |
| Price health | $0.50–$40.00 per GB broad parser guardrail | Values outside the guardrail |
The broad guardrail is designed to catch parsing errors and accessory/bundle mismatches, not suppress a real market move. Excluded observations keep a reason code in the private database.
3. Basket construction
The target is six active products: three 32GB kits and three 64GB kits. Ranking prioritizes recent purchase activity, rating count, star rating, Prime availability, and explicit technical identity—not the lowest price. Selection takes one product per brand before allowing a second product from the same brand.
Before ranking, titles are mapped to product families such as Kingston FURY Beast, G.Skill Flare X5, and G.Skill Trident Z5 Neo. Only one member of a family can represent a capacity. When both pass every gate, the non-RGB version is preferred over its RGB or colour variant.
An active product is removed immediately when a current search exposes a hard quality failure. Otherwise it is paused after six missed searches—about two weeks—and a qualified current replacement can enter the basket. Historical observations remain intact.
4. Weekly aggregation, mean, and median
Retail searches run Monday, Wednesday, and Friday. Each eligible product first becomes a comparable nominal-dollar value:
A product’s weekly value is the median of its valid checks during the Monday-through-Sunday UTC week. For n eligible active products, the published mean is the sum of those product-week USD/GB values divided by n. The published median is their middle sorted value—or the average of the two middle values when n is even. We publish both because the mean reacts more to a broad move while the median describes the center more robustly.
5. The rebased index
The first valid live observation is 100. On later weeks, the collector calculates current/previous price relatives for products present in both successful observations. The previous index is multiplied by the mean or median overlapping-product relative. If no products overlap, the previous index level is carried forward and the overlap count exposes the break.
Dollar-per-GB values remain the primary result. The rebased index is a continuity aid, not a way to conceal basket composition.
6. Data-health labels
Good means at least four eligible active products from at least three brands. Thin means a valid point exists with less breadth. Initializing means no valid point exists. A timestamp always identifies the latest successful run.
7. Collection and quality checks
Scheduled observations run Monday, Wednesday, and Friday. Each run uses a broad and a mainstream-brand search for both capacities. Four healthy requests per run refresh prices, demand evidence, and replacement candidates—about 52 requests per average month against the primary provider’s 100-request tier.
Large price changes, new basket members, and routine sample checks receive BrowserFetcher verification through rotating private sticky sessions. The verifier blocks expensive resources, records bytes, stops on challenges, and has a 75 MB monthly ceiling. Proxy results never turn an unknown offer into a guessed price.
8. One-year historical backcast
The default trend begins in August 2025 with four established desktop DDR5 kits: Corsair Vengeance and Crucial Pro at 32GB, plus Kingston FURY Beast and G.Skill Trident Z5 Neo RGB at 64GB. Their dated public product histories come from PriceHistory.app.
When multiple values exist on one date, the last published value for that date is retained while every same-day value remains in the audit note. A price is carried forward for at most 45 days. Each product-month must cover at least 15 days, except the partial August 2026 bridge month, and becomes the median of its applicable daily prices divided by kit capacity.
The monthly backcast uses the same overlapping-product price-relative calculation as the weekly live index. The historical series is rebased to 100 at the August 10, 2026 handoff; the live series starts at 100 there. A vertical marker identifies the change from the four-product historical source basket to the six-product live MPC basket. This makes the trend comparable while keeping the source and basket change explicit.
The historical basket measures trend, not an exact dollar estimate for the live six-kit basket. The older Stanford DAM cheapest-retail series remains stored as external research context but is no longer the default chart line.
9. Known limitations
- Listed prices are not confirmed transactions.
- Sales tax is excluded; shipping is excluded unless a future source exposes it consistently.
- Retail availability and product selection can change between observations.
- Timing, speed, warranty, seller, and performance differences are not quality-adjusted.
- The index represents eligible US retail listings, not every retailer or the entire RAM market.
- Weekly data is not an intraday quote and does not predict the next move.
10. Revisions
backcast-v1-four-kit adds the August 2025–August 2026 historical reconstruction and explicit calculation-handoff marker. retail-v2-weekly established the launch baseline on August 12, 2026 with three observations per week and weekly product medians. retail-v3-mainstream replaced that same baseline week’s basket with a strict four-brand universe, private market-evidence and stock gates, compatibility exclusions, brand-first diversification, and product-family deduplication so cosmetic variants cannot receive separate weight. Product-level Amazon rating, review, and purchase-volume signals are used for screening but are not reproduced in the public basket.