Methodology & sources

What the index measures

The RarestMarket Premium Car Index tracks price levels for used premium and luxury cars across the open Nordic market. The basis is observed asking prices — what sellers ask, not what cars sell for. This is always disclosed, and every published figure carries its sample size (n) and period.

New cars are excluded: new-car prices follow list prices and would distort used-market statistics.

For makes whose entire range is premium (Porsche, Ferrari, Bentley etc.), all models are included. For volume makes, only the performance and flagship models count: BMW M2–M8, Audi RS models and the R8, genuine Mercedes-AMG (not AMG-Line trim), G-Class and Maybach, Tesla Model S/X, Range Rover and Defender, and Volvo EX90/XC90. A 320d with an M-Sport package is not a premium car and is not counted.

Sources and collection

Price points are collected from Blocket (Sweden), Finn.no (Norway) and RarestMarket's own inventory, plus AutoScout24 (Germany) as an import reference. We store only facts about each observation — make, model, model year, mileage, price, currency, fuel, seller type, location, and when the ad was first and last observed. Ad copy and images from external sources are never stored or republished. Collection runs at low frequency with a bounded number of pages per run; the index is built on a representative sample, not total surveillance.

Duplicates

The same car is often listed on several sites. Observations are merged by registration number/VIN when known, otherwise by a fingerprint of make, model, model year, mileage (rounded to the nearest 5,000 km) and power. Two distinct cars with identical specs may occasionally merge incorrectly — which slightly underestimates n, the conservative direction to err in.

Models and special editions

Each observation is classified to a canonical model (generation prefixes like "718" and trim words are normalized away) and, where relevant, a variant. Standard versions (Carrera, S, 4S, GTS) count toward the model median. Special editions that trade on rarity or track pedigree — GT3, GT3 RS, GT4 RS, Turbo S, Turbo GT and the like — are split out, excluded from the model median and reported on their own pages.

Why: a median for "911" that mixes a base Carrera with a GT3 RS is misleading. To classify special editions correctly, power is read from the listing's detail page for cars whose title carries a GT/RS/Turbo S badge.

Import reference (Germany)

Many Nordic premium-car buyers import from Germany. We therefore also collect German asking prices from AutoScout24 as a separate import reference. These figures are reported in euros (with an approximate SEK conversion) and kept strictly apart from the Nordic market — they never enter the Nordic median or the composite index, but are shown as a comparison on the model and variant pages.

The comparison is of asking prices and does not account for shipping, VAT, import duties or registration — it shows the market picture, not your final bill.

Normalization

Mileage is always stored in kilometres (the Swedish "mil" is multiplied by 10). Prices are reported in SEK for Sweden and NOK for Norway. Amounts converted between currencies (Nordic-wide figures and the German import reference) use the ECB official reference rates as a MONTHLY AVERAGE of the period's daily rates — not a single day's rate — for a stable, reproducible figure. The rate and its source (ECB average or fallback) are stored on every published row.

Thresholds and frozen months

Statistics are published per segment (market, make, model × Sweden/Norway/Nordics) only when the sample suffices: at least 10 unique cars for market figures and 5 for make and model figures. Breakdowns (model year, mileage band, fuel) require at least 3 cars per row. Figures are computed per calendar month. The current month updates continuously; once a month closes its figures are frozen and never retroactively changed — a cited number must remain reproducible forever.

Outliers

Obvious data errors (e.g. a missing zero in the price) are filtered out before computation: per make, observations more than 10× above or below the make's median price are discarded — a deliberately wide gate that only typo-level errors fail. Published price spans are furthermore P5–P95 (the middle 90% of the market), not absolute low–high, so a single mispriced listing never defines the span. Raw min/max remain in the data export for transparency.

The composite index

The index value is 100 in the base month (the first published month). For each later month, the ratio of that month's to the base month's median price is computed per make (only makes with sufficient n in both months), and the index is 100 × the median of those ratios. Medians at both levels make the index robust to outliers and to supply-mix shifts between months.

Time on market

When an ad disappears from a source we crawled exhaustively, the observation is marked delisted. Median time on market measures days from first to last observation for ads delisted during the month. Delisting approximates a sale — cars can also be withdrawn for other reasons, a known limitation.

License and citation

All published index data may be reused freely under CC BY 4.0 with attribution to "RarestMarket Premium Car Index" and a link to this page. The data is also machine-readable as JSON and CSV via /api/market-index.

Methodology version: 1.0. Changes to universe, thresholds or computation produce a new version; older series remain untouched.