Porsche P.I.
Back-test

Appraisals against outcomes

44 sold cars with both an estimate and a result · 16 reserve-not-met listings shown but not scored · 1 appraisal still awaiting an outcome

Scored across 2 versions of the appraisal prompt — before revisions were recorded (41), b2519c2a (3). The prompt carries a calibration note built from this page, so the figures below average two different estimators.

Inside the range
57%
25 of 44
Typical miss
12.4%
median, unsigned
Within 10%
45%
35 within 20%
Lean
-7.5%
estimates run low
-40%-20%0%+20%+40% 2005 Honda S2000 Track Car +23.3% 2005 Honda S2000 Track Car — estimated $26,500, made $21,500 31k-Mile 2000 Dodge Viper GTS +16.8% 31k-Mile 2000 Dodge Viper GTS — estimated $66,000, made $56,500 36k-Mile 2015 Porsche Cayman GTS 6-Sp… +16.6% 36k-Mile 2015 Porsche Cayman GTS 6-Speed Track Car — estimated $58,000, made $49,750 2007 Porsche 911 Carrera 4S Cabriolet… +16.3% 2007 Porsche 911 Carrera 4S Cabriolet 6-Speed — estimated $50,000, made $42,997 20k-Mile 2008 Honda S2000 +13.9% 20k-Mile 2008 Honda S2000 — estimated $39,000, made $34,250 2003 Porsche 911 GT2 +12.6% 2003 Porsche 911 GT2 — estimated $296,000, made $262,777 9k-Mile 2011 Audi R8 V10 Spyder 6-Spe… +9.0% 9k-Mile 2011 Audi R8 V10 Spyder 6-Speed — estimated $158,000, made $145,000 37k-Mile 2000 Porsche Boxster S 6-Spe… +5.4% 37k-Mile 2000 Porsche Boxster S 6-Speed — estimated $19,500, made $18,500 2001 Jeep Cherokee Sport 4×4 +5.0% 2001 Jeep Cherokee Sport 4×4 — estimated $10,500, made $10,000 2002 Porsche Boxster S 6-Speed +4.3% 2002 Porsche Boxster S 6-Speed — estimated $12,250, made $11,750 28k-Mile 2001 Porsche 911 Turbo Coupe… +3.7% 28k-Mile 2001 Porsche 911 Turbo Coupe 6-Speed — estimated $97,000, made $93,500 2025 Porsche 718 Spyder RS Weissach -0.5% 2025 Porsche 718 Spyder RS Weissach — estimated $194,000, made $195,000 9k-Mile 2000 Honda S2000 -1.1% 9k-Mile 2000 Honda S2000 — estimated $44,500, made $45,000 40k-Mile 2004 Honda S2000 -2.0% 40k-Mile 2004 Honda S2000 — estimated $36,000, made $36,750 2008 Porsche 911 Turbo Coupe 6-Speed -3.6% 2008 Porsche 911 Turbo Coupe 6-Speed — estimated $134,000, made $139,000 23k-Mile 2005 Honda S2000 -3.9% 23k-Mile 2005 Honda S2000 — estimated $36,500, made $38,000 1999 Porsche Boxster 5-Speed -4.4% 1999 Porsche Boxster 5-Speed — estimated $10,750, made $11,250 19k-Mile 2011 Porsche Boxster S 6-Spe… -5.2% 19k-Mile 2011 Porsche Boxster S 6-Speed — estimated $46,000, made $48,500 2003 Acura NSX-T 6-Speed -5.7% 2003 Acura NSX-T 6-Speed — estimated $133,000, made $141,000 24k-Mile 2006 Ford GT -5.8% 24k-Mile 2006 Ford GT — estimated $452,000, made $480,000 1,500-Mile 2022 Cadillac CT5-V Blackw… -6.2% 1,500-Mile 2022 Cadillac CT5-V Blackwing 6-Speed — estimated $83,000, made $88,500 8k-Mile 2007 Porsche 911 Turbo Coupe … -6.7% 8k-Mile 2007 Porsche 911 Turbo Coupe 6-Speed — estimated $196,000, made $210,000 13k-Mile 2006 Honda S2000 -7.4% 13k-Mile 2006 Honda S2000 — estimated $56,500, made $61,000 2004 Porsche 911 Turbo Cabriolet 6-Sp… -9.4% 2004 Porsche 911 Turbo Cabriolet 6-Speed — estimated $58,000, made $64,000 26k-Mile 2001 Honda S2000 -9.8% 26k-Mile 2001 Honda S2000 — estimated $29,750, made $33,000 Modified 2007 Porsche Cayman 5-Speed -9.9% Modified 2007 Porsche Cayman 5-Speed — estimated $20,500, made $22,750 Viola Metallic 2021 Porsche 718 Spyde… -11.1% Viola Metallic 2021 Porsche 718 Spyder 6-Speed — estimated $142,000, made $159,718 4,300-Mile 2009 Dodge Viper SRT-10 Ro… -12.2% 4,300-Mile 2009 Dodge Viper SRT-10 Roadster — estimated $86,000, made $98,000 1998 Porsche Boxster 5-Speed -12.5% 1998 Porsche Boxster 5-Speed — estimated $14,000, made $16,000 36k-Mile 2012 Audi R8 V10 Coupe 6-Spe… -12.9% 36k-Mile 2012 Audi R8 V10 Coupe 6-Speed Conversion — estimated $101,000, made $116,000 26k-Mile 2002 Honda S2000 -14.9% 26k-Mile 2002 Honda S2000 — estimated $31,500, made $37,000 36k-Mile 2008 Porsche 911 Carrera S C… -16.9% 36k-Mile 2008 Porsche 911 Carrera S Cabriolet 6-Speed — estimated $61,500, made $74,000 22k-Mile 2010 Porsche Cayman 6-Speed -18.0% 22k-Mile 2010 Porsche Cayman 6-Speed — estimated $36,500, made $44,500 2011 Porsche Boxster S 6-Speed -18.1% 2011 Porsche Boxster S 6-Speed — estimated $30,500, made $37,250 39k-Mile 2008 Porsche 911 Turbo Coupe… -18.5% 39k-Mile 2008 Porsche 911 Turbo Coupe 6-Speed — estimated $108,000, made $132,500 2008 Porsche Cayman S 6-Speed -19.7% 2008 Porsche Cayman S 6-Speed — estimated $24,500, made $30,500 2000 Porsche Boxster -20.4% 2000 Porsche Boxster — estimated $10,750, made $13,500 One-Family-Owned 1999 Jeep Cherokee S… -22.4% One-Family-Owned 1999 Jeep Cherokee Sport 4×4 — estimated $29,500, made $38,000 2008 Porsche Cayman -23.1% 2008 Porsche Cayman — estimated $12,500, made $16,250 One-Owner, 23k-Mile 1999 Acura NSX Za… -23.6% One-Owner, 23k-Mile 1999 Acura NSX Zanardi Edition #22 — estimated $480,000, made $628,000 Safari-Style 2010 Porsche 911 Carrera… -28.9% Safari-Style 2010 Porsche 911 Carrera 4S Coupe — estimated $59,000, made $83,000 2006 Porsche Boxster S 6-Speed -31.0% 2006 Porsche Boxster S 6-Speed — estimated $24,500, made $35,500 20k-Mile 2001 RUF 3400 S -31.8% 20k-Mile 2001 RUF 3400 S — estimated $150,000, made $220,000 8-Mile, One-Owner 2006 Ford GT Herita… -39.3% 8-Mile, One-Owner 2006 Ford GT Heritage Edition — estimated $1,275,000, made $2,101,000
Estimate against the realised price, per car. Bars right of zero were over-estimated, left under-estimated. Solid bars finished outside the range the appraisal stated (19 of 44); outlined bars landed inside it.

Is reading the car worth it?

A typical miss of 12.4% means nothing on its own — it has to be against something. The row below it is the same question answered without opening a single listing: take the comparables the model was handed and quote their median. The bid is not a forecast at all, and sits here as the floor.

EstimatorCarsTypical missLean
The appraisal Claude, reading the car against the comparables and the dossier 44 12.4% -7.5%
Median of the comparables the same cars, no reading of the subject at all 44 20.7% -3.5%
The bid when appraised where bidding stood, not a forecast — the gap is what lands late 43 43.4% -42.6%

Reading: The appraisal beats the do-nothing estimate by 8.4 points (40% tighter): 12.4% against 20.7%. That gap is what reading the car and its thread is actually worth.

By how much of the auction was left

The prompt asks for the price a car finishes at, and BaT bidding is back-loaded, so an estimate made two days out is a harder call than one made an hour out. If that is working, the miss should shrink down this table.

Lead timeCarsIn rangeTypical miss
Under 6 hours6 67% 8.4%
6–24 hours5 40% 18.0%
1–3 days9 33% 16.8%
Over 3 days24 67% 8.2%

Are the comparables stale?

The estimates lean low. Two different things produce that same lean, and the appraisal prompt currently attributes all of it to one of them — special cars priced as ordinary ones. The other is arithmetic rather than judgement: comparables are the newest N analysed sales, a count window rather than a time window, so on a model that trades thinly they can reach back years. Anchor on cars that sold into an older market and the estimate lands behind it, however well the car itself was read. These two figures separate the explanations. Signed error is used throughout — drift has a direction, and taking absolute values would erase exactly what is being looked for.

Age of the comparables
not testable
r = 0.33 rests on one car (43% of the fit) · n=44
The model's own year-on-year move
not testable
r = -0.16 rests on one car (18% of the fit) · n=43

Reading: The anchors barely vary, so this cannot be tested: almost every appraisal was made against comparables of much the same age, and a line fitted across that rests on one or two stragglers rather than on a trend. Comparable age spans only 0.0–1.9 years across 44 cars, and one of them carries 43% of the fit. Stale comparables are not ruled out — they are simply not what these cars can speak to.

Age of the comparablesCars Mean signed errorIn range
Under 6 months40 -9.1% 57%
6–12 months2 +1.4% 100%
1–2 years2 +14.6% 0%

Comparable age is the median age, at the time of the appraisal, of the sales the model named as its anchors — 44 of the scored cars. The block is reconstructed from the sales on file rather than replayed from the prompt, which is exact on a liquid model and can read slightly old on a thin one, where a car analysed after the fact now falls inside the window. The trend figure is that model's own year-on-year median change from whichever run sits closest in time to the appraisal. p is a seeded permutation test, so it does not move between runs, and at this sample size it is a brake on over-reading rather than a finding of its own.

Every appraisal with a known outcome

CarRangeEstimateRealised ErrorBandLeadComp ageResult
8-Mile, One-Owner 2006 Ford GT Heritage Edition $1,100,000–$1,500,000 $1,275,000 $2,101,000 -39.3% outside 3.7d 3mo sold
20k-Mile 2001 RUF 3400 S $95,000–$215,000 $150,000 $220,000 -31.8% outside 5.9d 1mo sold
2006 Porsche Boxster S 6-Speed $20,500–$28,500 $24,500 $35,500 -31.0% outside 3.1d 2mo sold
Safari-Style 2010 Porsche 911 Carrera 4S Coupe $48,000–$74,000 $59,000 $83,000 -28.9% outside 6.7d 4mo sold
One-Owner, 23k-Mile 1999 Acura NSX Zanardi Edition … $430,000–$560,000 $480,000 $628,000 -23.6% outside 12h 3mo sold
2005 Honda S2000 Track Car $21,500–$32,000 $26,500 $21,500 +23.3% in range 23h 2mo sold
2008 Porsche Cayman $9,500–$15,500 $12,500 $16,250 -23.1% outside 2h 3mo sold
One-Family-Owned 1999 Jeep Cherokee Sport 4×4 $24,500–$35,000 $29,500 $38,000 -22.4% outside 6.1d 2mo sold
2000 Porsche Boxster $8,800–$13,000 $10,750 $13,500 -20.4% outside 1.9d 1mo sold
2008 Porsche Cayman S 6-Speed $410–$29,000 $24,500 $30,500 -19.7% outside 1.1d 1mo sold
39k-Mile 2008 Porsche 911 Turbo Coupe 6-Speed $95,000–$122,000 $108,000 $132,500 -18.5% outside 4.7d 1mo sold
2011 Porsche Boxster S 6-Speed $25,500–$35,500 $30,500 $37,250 -18.1% outside 1.1d 2mo sold
22k-Mile 2010 Porsche Cayman 6-Speed $30,000–$43,000 $36,500 $44,500 -18.0% outside 19h 0mo sold
36k-Mile 2008 Porsche 911 Carrera S Cabriolet 6-Spe… $54,000–$70,000 $61,500 $74,000 -16.9% outside 2.5d 1mo sold
31k-Mile 2000 Dodge Viper GTS $57,000–$75,000 $66,000 $56,500 +16.8% outside 2.1d 2mo sold
36k-Mile 2015 Porsche Cayman GTS 6-Speed Track Car $50,000–$66,000 $58,000 $49,750 +16.6% outside 2.9d 1.9y sold
2007 Porsche 911 Carrera 4S Cabriolet 6-Speed $43,000–$57,000 $50,000 $42,997 +16.3% outside 4.7d 1mo sold
26k-Mile 2002 Honda S2000 $27,500–$35,500 $31,500 $37,000 -14.9% outside 4.1d 1mo sold
20k-Mile 2008 Honda S2000 $34,000–$45,000 $39,000 $34,250 +13.9% in range 5.0d 1mo sold
36k-Mile 2012 Audi R8 V10 Coupe 6-Speed Conversion $88,000–$117,000 $101,000 $116,000 -12.9% in range 6.1d 1mo sold
2003 Porsche 911 GT2 $268,000–$340,000 $296,000 $262,777 +12.6% outside 19h 1.9y sold
1998 Porsche Boxster 5-Speed $11,500–$17,000 $14,000 $16,000 -12.5% in range 3.0d 1mo sold
4,300-Mile 2009 Dodge Viper SRT-10 Roadster $76,000–$98,000 $86,000 $98,000 -12.2% in range 0h 4mo sold
Viola Metallic 2021 Porsche 718 Spyder 6-Speed $132,000–$155,000 $142,000 $159,718 -11.1% outside 1h 3mo sold
Modified 2007 Porsche Cayman 5-Speed $16,500–$25,500 $20,500 $22,750 -9.9% in range 3.8d 0mo sold
26k-Mile 2001 Honda S2000 $27,000–$33,000 $29,750 $33,000 -9.8% in range 12h 1mo sold
2004 Porsche 911 Turbo Cabriolet 6-Speed $48,000–$68,000 $58,000 $64,000 -9.4% in range 2.8d 3mo sold
9k-Mile 2011 Audi R8 V10 Spyder 6-Speed $145,000–$174,000 $158,000 $145,000 +9.0% in range 6.1d 9mo sold
13k-Mile 2006 Honda S2000 $48,000–$66,000 $56,500 $61,000 -7.4% in range 5.8d 1mo sold
8k-Mile 2007 Porsche 911 Turbo Coupe 6-Speed $172,000–$222,000 $196,000 $210,000 -6.7% in range 5.8d 2mo sold
1,500-Mile 2022 Cadillac CT5-V Blackwing 6-Speed $76,500–$90,000 $83,000 $88,500 -6.2% in range 3.0d 9mo sold
24k-Mile 2006 Ford GT $415,000–$495,000 $452,000 $480,000 -5.8% in range 9.7d 2mo sold
2003 Acura NSX-T 6-Speed $118,000–$148,000 $133,000 $141,000 -5.7% in range 1h 3mo sold
37k-Mile 2000 Porsche Boxster S 6-Speed $16,500–$23,000 $19,500 $18,500 +5.4% in range 6.9d 1mo sold
19k-Mile 2011 Porsche Boxster S 6-Speed $40,000–$52,000 $46,000 $48,500 -5.2% in range 3h 2mo sold
2001 Jeep Cherokee Sport 4×4 $8,000–$13,000 $10,500 $10,000 +5.0% in range 3.2d 3mo sold
1999 Porsche Boxster 5-Speed $8,500–$13,500 $10,750 $11,250 -4.4% in range 6.0d 1mo sold
2002 Porsche Boxster S 6-Speed $10,500–$14,000 $12,250 $11,750 +4.3% in range 4.9d 1mo sold
23k-Mile 2005 Honda S2000 $32,000–$41,000 $36,500 $38,000 -3.9% in range 6.8d 2mo sold
28k-Mile 2001 Porsche 911 Turbo Coupe 6-Speed $84,000–$115,000 $97,000 $93,500 +3.7% in range 2.8d 1mo sold
2008 Porsche 911 Turbo Coupe 6-Speed $118,000–$152,000 $134,000 $139,000 -3.6% in range 7.0d 1mo sold
40k-Mile 2004 Honda S2000 $31,500–$40,500 $36,000 $36,750 -2.0% in range 6.8d 1mo sold
9k-Mile 2000 Honda S2000 $38,000–$52,000 $44,500 $45,000 -1.1% in range 5.0d 2mo sold
2025 Porsche 718 Spyder RS Weissach $184,000–$204,000 $194,000 $195,000 -0.5% in range 2h 6mo sold
2012 Ferrari 458 Spider $225,000–$292,000 $255,000 $245,000 — not scored 1.6d 6mo RNM
2,500-Mile 2013 Ferrari 458 Spider $370,000–$495,000 $428,000 $405,000 — not scored 1.5d 2mo RNM
28k-Mile 2006 Porsche 911 Carrera 4S Coupe 6-Speed $65,000–$89,000 $77,000 $67,500 — not scored 5.8d 4mo RNM
21k-Mile 2005 Porsche 911 Turbo Cabriolet 6-Speed $74,000–$104,000 $88,000 $80,500 — not scored 1.9d 3mo RNM
15k-Mile 2001 Honda S2000 $29,000–$40,000 $34,000 $36,000 — not scored 1.8d 2mo RNM
9k-Mile 2009 Dodge Viper SRT-10 Roadster $62,000–$90,000 $75,000 $58,000 — not scored 2.9d 5mo RNM
20k-Mile 2001 Dodge Viper GTS ACR $68,000–$90,000 $78,000 $74,501 — not scored 1.1d 5mo RNM
11k-Mile 2002 Dodge Viper GTS Final Edition $64,000–$86,000 $74,000 $76,251 — not scored 1h 2mo RNM
19k-Mile 2007 Porsche 911 Turbo Coupe 6-Speed $132,000–$172,000 $152,000 $146,000 — not scored 6.0d 1mo RNM
2025 Porsche 718 Spyder RS Weissach $176,000–$208,000 $192,000 $180,000 — not scored 4.0d 6mo RNM
25k-Mile 2010 Porsche 911 Turbo Cabriolet 6-Speed $122,000–$158,000 $140,000 $177,177 — not scored 2.7d 3mo RNM
41k-Kilometer 2008 Porsche 911 GT3 $118,000–$168,000 $142,000 $115,000 — not scored 3.1d 1mo RNM
32k-Mile 2008 Porsche Boxster 5-Speed $18,500–$25,000 $21,500 $22,532 — not scored 4.1d 2mo RNM
20k-Mile, Supercharged 2006 Porsche 911 Carrera S C… $54,000–$73,000 $63,000 $77,997 — not scored 3.6d 2mo RNM
20k-Mile 2012 Audi R8 GT Spyder V10 $110,000–$160,000 $135,000 $103,000 — not scored 1h 1mo RNM
37k-Mile 2005 Porsche 911 Turbo S Cabriolet 6-Speed $78,000–$103,000 $90,000 $96,000 — not scored 20h 1mo RNM

Realised is the hammer price for a sold car. For a reserve-not-met listing it is the highest bid the car failed to sell at, which is not a clearing price — those rows are listed for completeness and excluded from every figure above, because counting them would flatter the estimates on exactly the cars the market disagreed about.

A sample this size supports no strong claim about accuracy. It is here so the estimates can be checked at all, and so a pattern across similar cars is visible when one appears.

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