Methodology

What Is SilphCo Price?#

Most price sites show the last sale — noisy for illiquid Pokemon cards where a Charizard PSA 10 can swing from $9,200 to $17,500 in a week. SilphCo Price smooths that noise with a time-value weighted average (TV-WAP). Recent sales count more than old ones, outliers are automatically rejected, and missing grades are inferred from nearby grades using historical premium ratios.

Adaptive Windows#

A Charizard Base PSA 10 trades dozens of times a month; a vintage PSA 10 might trade once a year. A single fixed window would overreact for one and ignore the other. SilphCo Price uses an adaptive half-life based on trailing 30-day volume to scale the lookback window automatically:

Outlier Rejection#

A $50,000 Charizard sale might be a wash trade, a typo, or a bundled deal. SilphCo Price uses a modified Z-score filter to detect and exclude these outliers before averaging — conservative enough to catch genuine anomalies without discarding legitimate market moves.

Confidence Levels#

Every SilphCo Price carries a tvwap_confidence label. This tells you how the price was derived and how much weight to give it.

direct and direct_offchain prices are backed by actual sales. set_estimate and grader_estimate are directional only — useful for trends, not for setting exact listing prices.

Grade Inference#

Not every grade trades regularly. A PSA 10 Charizard sells weekly, but a PSA 8 can go months between sales. Rather than showing a stale price, SilphCo infers it from nearby grades using historical premiums — computed from 90-day co-occurrence data, falling back to set-level medians then global defaults.

Rules of thumb:

• We never infer across more than 2 grade steps (PSA 10 can infer PSA 9 and PSA 8, but not PSA 7).
• Collectible grades (8–10) never mix with low grades (1–6) — the markets behave differently.
• Inferred prices never feed further inference. A PSA 9 inferred from PSA 10 will not be used to infer PSA 8.

On-Chain vs Off-Chain#

SilphCo blends two sources of sales data:

On-chain is primary. If it is fresh, we use it. If stale or missing, off-chain fills the gap. Both sources run through the same TV-WAP engine so they are directly comparable.

Staleness#

Every SilphCo Price carries a staleness score from 0 to 1:

• 1.0 — Very fresh. Sales within the adaptive window.
• 0.5 — Borderline. Sales exist but are aging.
• Below 0.5 — Stale. The UI shows "Estimated" to warn you the underlying data is old.

Staleness is the weighted average age of sales relative to the adaptive half-life. A 14-day-window card with its last sale 10 days ago is fresher than a 90-day-window card with its last sale 60 days ago.

Momentum#

When a card shows a statistically significant trend, SilphCo attaches a momentum signal.

We reconstruct weekly TV-WAP snapshots going back twice the adaptive half-life and fit a trend line. If the slope is strong enough to distinguish from noise, we label it Up or Down. If not, we label it Flat with no directional signal.

The forecast horizon matches liquidity: fast-trading cards get a 7-day forecast, sparse cards up to 45 days. Confidence bands widen with less data — wide at 4 snapshots (reflecting genuine uncertainty), narrowing as more history accumulates.