Consumer Price Index - Revision history

Admin: Redact exact basket weights and manipulation-defense thresholds (keep page substance)

2026-07-21T12:11:37Z

Redact exact basket weights and manipulation-defense thresholds (keep page substance)

← Older revision		Revision as of 12:11, 21 July 2026
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	{\| class="wikitable" style="width:100%;"		{\| class="wikitable" style="width:100%;"
	\|-		\|-
	! Category ~~!! Weight~~ !! Key items		! Category !! Key items
	\|-		\|-
	\| Building materials ~~\|\| 20%~~ \|\| Cobblestone, stone, deepslate, logs, planks, sand, glass		\| Building materials \|\| Cobblestone, stone, deepslate, logs, planks, sand, glass
	\|-		\|-
	\| Basic inputs ~~\|\| 30%~~ \|\| Iron ingot ~~(12%)~~, coal ~~(6%)~~, copper ~~(4%)~~, gold ~~(4%)~~, redstone ~~(4%)~~		\| Basic inputs \|\| Iron ingot, coal, copper, gold, redstone
	\|-		\|-
	\| Food and farming ~~\|\| 20%~~ \|\| Wheat, potato, carrot, cooked meats, sugar cane		\| Food and farming \|\| Wheat, potato, carrot, cooked meats, sugar cane
	\|-		\|-
	\| Utility consumables ~~\|\| 15%~~ \|\| Arrow, torch, firework rocket, lapis lazuli		\| Utility consumables \|\| Arrow, torch, firework rocket, lapis lazuli
	\|-		\|-
	\| Premium commodities ~~\|\| 15%~~ \|\| Diamond ~~(8%)~~, emerald ~~(3%)~~, netherite scrap ~~(4%)~~		\| Premium commodities \|\| Diamond, emerald, netherite scrap
	\|}		\|}

	~~Diamond is weighted at 8%, not higher~~ — the basket is ~~deliberately~~ tilted toward staples so a few large ~~diamond~~ trades cannot distort the signal.		Premium items carry deliberately modest weights — the basket is tilted toward staples so a few large trades cannot distort the signal. The exact weights are internal.

	== Index formula ==		== Index formula ==
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	: '''P = exp( SUM of weight_i x ln(price_i_trimmed) )'''		: '''P = exp( SUM of weight_i x ln(price_i_trimmed) )'''

	Each item's observed unit prices are sorted, then the ~~top and bottom 10%~~ are clamped (winsorized) before the geometric mean is computed. This prevents a single outlier trade from skewing the index.		Each item's observed unit prices are sorted, then the extreme tails are clamped (winsorized) before the geometric mean is computed. This prevents a single outlier trade from skewing the index.

	== Data source ==		== Data source ==
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	=== Depth gates ===		=== Depth gates ===
	An item is excluded from the policy basket unless it ~~meets all three~~ thresholds:		An item is excluded from the policy basket unless it clears minimum thresholds for transaction depth and for the number of unique buyers and sellers in the window. The exact gates are internal.
	* 10+ transactions in the ~~7-day window~~
	* 3+ unique buyers
	* 3+ unique sellers

	Items below these thresholds still appear in <code>/market</code> with a low-confidence flag but do not influence the engine.		Items below these thresholds still appear in <code>/market</code> with a low-confidence flag but do not influence the engine.

	=== Rate-of-change clamp ===		=== Rate-of-change clamp ===
	No single item can move ~~more~~ than ~~8% per week~~. Excess movement is dampened.		No single item can move faster than an internal weekly limit. Excess movement is dampened.

	=== Manipulation risk score ===		=== Manipulation risk score ===
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	# Low buyer diversity		# Low buyer diversity
	# Low seller diversity		# Low seller diversity
	# Account concentration (~~one~~ account ~~over 60% of volume~~)		# Account concentration (volume dominated by a single account)
	# Category outlier (~~item moved more than 2 standard deviations from~~ its category)		# Category outlier (a price moving far out of line with its category)

	When risk ~~exceeds 0.5~~, upward price moves are partially dampened while downward moves are trusted. This reflects that most MC economy manipulation is bullish.		When risk is high, upward price moves are partially dampened while downward moves are trusted. This reflects that most MC economy manipulation is bullish.

	=== Median lag ===		=== Median lag ===
	The [[Simulated ChestShop]] reads a ~~CPI snapshot~~ '''~~7 days old~~''', not current~~. A manipulator would need to sustain artificial~~ prices ~~for over a week — expensive and risky~~.		The [[Simulated ChestShop]] reads a '''lagged''' CPI snapshot, not current prices, so short-lived price spikes never reach it.

	== Per-item confidence ==		== Per-item confidence ==

Maintenance script: 2026-06-10 staleness scan: tooltips retired, real AH fees, /trade status, PvP rules, CPI dual basket, eviction reclaim

2026-06-10T20:27:52Z

2026-06-10 staleness scan: tooltips retired, real AH fees, /trade status, PvP rules, CPI dual basket, eviction reclaim

← Older revision		Revision as of 20:27, 10 June 2026
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	A rising CPI means inflation. A falling CPI means deflation. A stable CPI means equilibrium.		A rising CPI means inflation. A falling CPI means deflation. A stable CPI means equilibrium.

			Since 2026-06-09 the system tracks '''two baskets''': the ''policy basket'' of curated staples described below (the cautious signal used for policy decisions), and an ''observed market basket'' built from what players actually trade, which adapts to real market activity.

	== Basket composition ==		== Basket composition ==

Maintenance script: Audit corrections from locked spec

2026-05-27T16:59:39Z

Audit corrections from locked spec

Show changes

Maintenance script: Initial content

2026-05-27T15:15:21Z

Initial content

New page

The '''Consumer Price Index''' (CPI) is a custom-built price tracking system on Prosperity SMP. It measures the cost of a fixed basket of goods using real player-to-player trade data, producing a single index number that represents the overall price level of the server economy. The CPI feeds directly into the [[Monetary policy engine]] and is reported weekly to the community via Discord.

== What the CPI measures ==
The CPI tracks the price of a weighted basket of 27 common items across five categories. It answers the question: "Are things getting more or less expensive on the server?"

A rising CPI means prices are going up (inflation). A falling CPI means prices are dropping (deflation). A stable CPI means the economy is in equilibrium.

== Basket composition ==
The policy CPI basket is weighted to reflect typical player spending patterns:

{| class="wikitable" style="width:100%;"
|-
! Category !! Weight !! Items
|-
| Building materials || 20% || Cobblestone, stone, deepslate, sand, gravel, logs, planks, sandstone, glass, bricks
|-
| Basic inputs || 30% || Iron ingot (12%), coal (6%), copper ingot (4%), gold ingot (4%), redstone (4%)
|-
| Food and farming || 20% || Wheat, potato, carrot, cooked beef, cooked chicken, cooked porkchop, sugar cane, paper
|-
| Utility consumables || 15% || Arrow, torch, firework rocket, lapis lazuli
|-
| Premium commodities || 15% || Diamond (8%), emerald (3%), netherite scrap (4%)
|}

Diamond is weighted at 8%, not 30% — the basket is deliberately tilted toward everyday staples rather than luxury items. A few large diamond trades should not distort the overall price signal.

== Index formula ==
The CPI uses a '''winsorized geometric mean''', the same mathematical approach used by real-world national statistics offices:

: '''P = exp( SUM of weight_i x ln(price_i_trimmed) )'''

Where each item price is winsorized (extreme outliers in the top and bottom 10% are clamped) before the geometric mean is computed. This prevents a single unusual trade from skewing the index.

== Data source ==
The CPI is computed exclusively from '''completed, non-simulated, player-to-player''' [[ChestShop]] transactions:

* Only real trades between players count. [[Simulated ChestShop]] activity is excluded.
* Only completed sales count. Listed prices (signs with no actual purchase) are tracked separately and do not affect the policy CPI.
* The rolling window covers the last 7 days of trade data.

This separation prevents a feedback loop where the [[Simulated ChestShop|Sim Shop]] buying activity inflates the CPI, causing the Sim Shop to buy at higher prices, causing CPI to rise further.

== Manipulation defenses ==
The CPI includes several custom-built defenses against price manipulation:

=== Depth gates ===
An item is excluded from the policy basket if it does not meet minimum thresholds:
* At least 10 transactions in the 7-day window
* At least 3 unique buyers
* At least 3 unique sellers

Items below these thresholds still appear in the <code>/market</code> command with a low-confidence flag, but they do not influence the engine.

=== Rate-of-change clamp ===
No item can move the CPI by more than 8% per week. If an item price jumps more than 8% from the prior week, the excess is attributed to possible manipulation and dampened.

=== Manipulation risk score ===
Each item receives a composite risk score based on five factors (each weighted equally at 0.20):

# Low transaction count (fewer than 10)
# Low buyer diversity (fewer than 3 unique buyers)
# Low seller diversity (fewer than 3 unique sellers)
# Account concentration (one account responsible for more than 60% of trade volume)
# Category outlier (item moved more than 2 standard deviations from its category average)

When the risk score exceeds 0.5, the system applies asymmetric trust dampening — upward price moves are partially discounted while downward moves are trusted at face value. This reflects the reality that most market manipulation in Minecraft economies is bullish (inflating prices to profit from the Sim Shop).

=== Median lag ===
The [[Simulated ChestShop]] reads a CPI snapshot that is '''7 days old''', not the current snapshot. This means a manipulator would need to sustain artificial prices for over a week before the Sim Shop adjusts — raising the cost and risk of manipulation.

== Per-item confidence ==
Each item in the basket receives its own confidence score:

: '''confidence = sqrt(depth_score x diversity_score)'''

Where depth_score reflects transaction count (maxes at 50 trades) and diversity_score reflects unique participant count (maxes at 8 unique buyers + sellers). Items with low confidence contribute less to the overall basket index.

== Player-facing: /market command ==
Players can check current market prices using <code>/market</code>:

{| class="wikitable"
|-
! Command !! What it shows
|-
| <code>/market</code> || Top 10 items by total dollar volume traded (last 7 days)
|-
| <code>/market <item></code> || Median price, fair range (25th-75th percentile), volume, category
|}

The <code>/market</code> command shows real player-to-player data only. It does '''not''' reveal the Sim Shop buy price, CentralBank balance, or engine recommendations.

== Weekly Discord report ==
Every Monday at midnight, an automated report posts to the server Discord with:
* Total items traded and turnover
* Top 10 items by value
* Per-item median prices

This report uses the same data pipeline as the policy CPI but is formatted as a public-facing summary.

== Commodity index ==
In addition to the policy CPI (which drives the [[Monetary policy engine]]), the system computes a separate '''commodity index''' tracking premium items (diamond, gold, netherite, emerald, ancient debris). This index is for dashboard display only and does not influence policy decisions.

== See also ==
* [[Monetary policy engine]] — the system that consumes the CPI
* [[Economy]] — how the economy works
* [[Simulated ChestShop]] — the market activity system (excluded from CPI)
* [[Trading]] — how trading works on the server
* [[ChestShop]] — the shop system that generates CPI data

[[Category:Systems]]