← How an Economy Grows and Why It Crashes
第 3 章 · 20 分钟
Prices and wages: the clearing mechanism, and when it is pinned
Price as information, and stickiness as an empirical claim.
概念地图
Price signal
Relative prices compress scattered scarcity into one number a decision-maker can act on.
深色为本章概念，浅色为其他章
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Locus01
延伸阅读
Hayek · 1945 · The Use of Knowledge in Society
Reads prices as a compression device: nobody needs to know why something became scarce, only that the number moved. He argued against the then-current claim that central calculation could substitute for markets; the cost is that the argument establishes what prices can carry, never how fast or how accurately they carry it.
Foundational
Keynes · 1936 · General Theory, chapters 2 and 19
Argued that nominal wages resist downward adjustment, so the labour market does not clear on its own. A direct reply to the line above, and the source of this chapter's dispute.
Turn
The menu-cost line · 1980s
Gave price stickiness a microfoundation: changing a price is itself costly, so not changing it under a small shock is rational. This turned stickiness from an assumption into a derived result, and moved the argument onto how large those costs are.
Revision
Schiff · 2010 · the chapters on falling prices
Holds that falling prices are the normal expression of rising productivity and that resisting them is the problem. The book does not distinguish price falls driven by productivity from price falls driven by collapsing spending; the first crack lands here.
Subject of this course
机制02
The compressor
Nobody on the island has counted the fish or the nets. Yet when fish get scarcer, what you must give up for one automatically rises, and everyone adjusts on that. Hayek called this the work of the price signal. It does not tell you why something is scarce, only how scarce. Every argument in the book about controls rests on this: fixing a price cuts the channel, which is a different thing from changing one allocation.
机制Scattered scarcity information, through one relative price, reaches every decision-maker.
可迁移性测试
Move it to emergency triage: a triage level compresses a patient's whole situation into one number the nurse can queue on, without knowing any full history. The isomorphism breaks in that a triage level is assigned by a person who can be held accountable, while a price is generated by trades and has no author.
机制03
The adjustment gate
Prices cannot always move at once. Relabelling costs something, reopening a contract costs something, and a pay cut damages morale. Together these form a gate: small shocks are stopped, prices hold, and quantities move first — output is cut, staff are let go. This is the core of the menu cost line. The book barely mentions it and assumes prices move freely; the derivation below shows that this default is precisely where it parts from its opponents.
机制Repricing cost, through blocking small adjustments, makes shocks land on quantities rather than prices.
可迁移性测试
Move it to airport scheduling: when runway capacity binds, the airport does not raise landing fees and let airlines sort it out — aircraft queue instead. Repricing is institutionally costly, so congestion shows up as delay rather than price. The isomorphism breaks in that airport fees are regulated, while most sellers set their own and face a lower gate.
Derivation04
From 'prices can move' to 'unemployment is voluntary'
What is being derived is a step the book implies and never states: why, inside its framework, persistent unemployment is nearly impossible.
Prices and wages adjust quickly after a shock
Chosen. The book assumes it holds, the Keynesian side assumes it does not, and the whole dispute unfolds from there.
Labour demand slopes downward
Chosen, and standard: the lower the wage, the more people are hired.
Workers accept any offer above their reservation wage
Chosen: it assumes no search frictions and no contract terms.
推导 · 0 / 4
裂缝05
Cracks in this framework
争议地形06
本书主张
Free adjustment of prices and wages is the channel through which an economy repairs itself. Falling prices are usually a normal result of rising productivity, and propping them up only blocks repair.
另一种看法
The Keynesian line holds that nominal wages are rigid downward, and that under heavy debt a price fall becomes self-reinforcing. Letting prices fall is then not repair but the amplification of a single shock into a contraction.
分歧扎在
The disagreement is rooted in one empirical claim — how fast nominal variables adjust — and not in values. Both sides agree prices carry information; they differ on how quickly the channel reopens after a shock.
什么证据能裁决
What would settle it is the shape of the nominal wage change distribution: if wages adjust freely, the distribution should be roughly symmetric; if there is downward rigidity, mass should pile up at zero and the negative side be shaved. Run that distributional test on individual wage records over many years and the answer is decidable for both sides.
The evidence points to rigidity that is real but not absolute: individual wage data in several countries do pile up at zero, while the share of negative changes rises in recessions. What is missing is direct evidence linking the pile-up to unemployment duration — the pile-up existing does not make it the cause.
Falsification07
The adjustment gate as a preregistrable test
The mechanism under test: repricing cost, through blocking small adjustments, makes shocks land on quantities.
Data source: item-level price series from retail scanner data, with same-store unit sales
Scanner data show the timing and size of every price change — one of the few settings where this mechanism is directly observable.
Sample: all categories of one retailer, with no filtering for 'price-sensitive' categories
Filtering by category turns the result into a description of the filter.
Window: weeks 1 to 13 after a cost shock such as a wholesale price change
Covers a typical repricing cycle and stays inside a season.
Threshold: the rise in repricing frequency after small cost shocks is significantly smaller than after large ones
The gate hypothesis says small shocks are stopped; the threshold is registered on that meaning.
Failure condition: no significant difference between the two, or small shocks trigger repricing more often
Either counts as refutation.
推导 · 0 / 3
接口08
Which slot it hangs on
挂在哪个槽位The conclusion you already hold is probably 'cheaper is good' — a judgement about your own purchasing power. This chapter goes at the layer above it: where the price fall came from.
Does this chapter (a) constrain 'cheaper is good', or (b) open a new slot about prices carrying information?
慢变量Register two slow variables: the distribution of nominal wage changes in the industry you follow (is there a pile-up at zero), and its debt-to-assets ratio. Look at the first one in a few days.
小结09
本章小结
01Prices work by compressing scattered information; fixing one cuts the channel, not just one allocation.
02'If wages keep falling some level clears' is an identity, not a virtue of markets.
03The empirical risk sits in how fast adjustment happens and whether unemployment comes only from regulation.
04The book runs productivity-driven price falls and debt deflation together as one thing.
05An 'eventual adjustment' claim with no deadline is self-consistent under every outcome.
提取练习 · 合上书，先自己答一遍。
?Is 'unemployment equals those willing to work minus those hired' (a) an identity or (b) an empirical claim?
?Does Fisher's debt deflation attack (a) the compressor mechanism or (b) the inference that falling prices are harmless?
Forced choice10
B · Identify the tag
'If wages can keep falling, some wage equates supply and demand' — what kind of step is that?
二选一
Forced choice11
C · Locate the crack
In which situation does this framework give a confident and wrong answer?
二选一
读到这里，把它记为已读。