In one sentence — In Chapter 9, Hurst describes a price change as the outcome of decisions influenced by fundamentals, chance, and a residual motivation called X. It is a historical framework from 1970, not a complete modern model of price formation.
Why do prices change according to Hurst?
Hurst begins with a direct idea: an observed price changes when buyers and sellers reach a trade. In his diagram, the investment decision receives several influences; a “conversion mechanism” then turns decisions into transactions and price changes.
This is the author's chosen abstraction. Orders, intermediaries, and the exchange sit inside one box because the chapter studies motives for decisions rather than explaining in detail how a market matches orders.
Three families of influence
Fundamentals
Hurst includes information about the company, its industry, and the broad economy. In his price-motion model, he assigns fundamentals about 75% of motion, mainly as a slow trend. These are Hurst's stated estimates, not modern measurements that hold for every market or period.
Random factors
A person may buy to place excess cash or sell to meet a personal need without reacting to the price level. Hurst treats these decisions as noise and assigns them about 2% of motion. This too is an estimate internal to the book.
X motivation
The remaining 23% is grouped under X motivation. Hurst associates it with the oscillatory component he believes he isolated, but he does not identify X's cause. It is therefore a residual in his framework, not the name of a demonstrated force.
What the chapter is trying to argue
Chapter 9 seeks to give readers confidence in the techniques presented earlier. Hurst argues that, if part of an oscillation has a repeatable structure, risk depends not only on trade duration but also on rule quality, entry timing, and expected error.
That is the author's thesis, not permission to treat short-term trading as safe. A cyclic forecast can fail; costs, liquidity, position size, and invalidation remain part of the decision.
The role of fundamentals
For Hurst, fundamentals have two roles. Company-specific news differentiates one security from another because it changes investors' expectations. Broad economic conditions may instead contribute to the market's underlying motion.
The book compares the centre line of the Dow Jones Industrial Average with gross national product and observes a correlation. It is a historical comparison selected by the author: correlation does not imply causation, nor does it prove that one economic indicator explains the market trend.
Hurst also uses wars, crises, and devaluations as examples in arguing that visible events do not explain all the regularity he attributes to cycles. The conclusion depends on the chosen periods, filters, and series; it does not demonstrate that news is irrelevant to prices.
The diagram's boundary
The “conversion mechanism” box compresses elements that matter to price formation: order types, available counterparties, liquidity, venue rules, and execution. The diagram is useful for reading Hurst's argument, but it is not a complete representation of how a market works.
This boundary prevents two mistakes. The first is confusing a decision with the price that will actually be executed. The second is treating the 75/23/2 shares as a universal decomposition rather than one author's historical proposal.
Where the evidence ends
The examples, filters, and DJIA decomposition in the book were constructed and assessed by the same author. They document the method's internal coherence on historical samples, but are not independent validation of the shares or X motivation.
Using this framework today requires a test stated in advance: defined data and rules, out-of-sample checking, comparison with a simple baseline, realistic costs, and a criterion for rejecting the hypothesis. The useful conclusion is not “prices are predictable”, but a testable question: which part of motion am I explaining, and which part am I leaving out?
Why the entry remains useful
Chapter 9 makes explicit the passage from information to decision and from decision to price. It also helps separate what Hurst observes, estimates, and hypothesizes—an essential distinction before studying the DJIA decomposition or psychological barriers.
Sources
- J. M. Hurst, The Profit Magic of Stock Transaction Timing, Prentice-Hall, 1970, Chapter 9, pp. 141–157 — decision diagram, three families of influence, and the author's argument.
- Google Books bibliographic record for the 1970 Prentice-Hall edition.
Connections
- Price-motion model — the historical 75/23/2 decomposition
- Cyclic X motivation — the residual and its causal limit
- Historical events and cyclicity — examples used by the author
- DJIA spectral decomposition — the internal demonstration to assess
- Hurst tradition — complete historical path