Sector groups and how they move

Sorting listed companies into sectors is an act of classification, and like every classification it is useful because of what it predicts rather than because it is true. What it predicts is shared sensitivity. Companies that sell the same thing, buy the same input, serve the same customer or borrow on the same terms tend to be repriced by the same news on the same day, and a sector label is a compact way of saying so. This guide covers how the classification is built, what each group is sensitive to, why grouped shares move as a block, and the several places where the label stops describing the company.

How the classification works 

The classifications used across the industry sort every listed company into one sector, then into progressively finer industry groups beneath it, on the basis of where the majority of its revenue comes from. The standard schemes use eleven top level sectors: energy, materials, industrials, consumer discretionary, consumer staples, health care, financials, information technology, communication services, utilities and real estate. Index providers and data vendors apply the same scheme, which is why a sector breakdown looks familiar wherever it is published.

One company sits in exactly one sector, which is the scheme's greatest convenience and its greatest weakness. A conglomerate with several unrelated businesses is assigned to whichever one is largest. A company that has changed shape over a decade may still carry the label of the business it used to be. And the sector boundaries themselves are periodically redrawn, which reassigns companies without anything about them changing, and mechanically changes every sector level statistic computed before and after.

What each group is sensitive to 

Energy companies sell a commodity whose price they do not set, so the crude and gas benchmarks reach Exxon Mobil Corp., Chevron Corp., Shell plc, BP plc and TotalEnergies on the same tick. Materials and mining companies stand in the same relationship to iron ore, copper and coal, which is why BHP Group, Rio Tinto, Glencore plc and Fortescue Ltd. move with Chinese construction and industrial data.

Financials are sensitive to interest rates in a direction that depends on the shape of the yield curve rather than on its level, and to credit conditions, which is why JPMorgan Chase & Co., Bank of America, HSBC Holdings, Barclays plc, Emirates NBD and Al Rajhi Bank react to rate decisions and to loan loss news together. Information technology and semiconductors are sensitive to capital spending cycles and, because a great deal of their value rests on earnings expected far in the future, to the discount rate applied to those earnings: NVIDIA Corp., TSMC, ASML Holding, Samsung Electronics, Broadcom Inc., Applied Materials and Lam Research form one of the tightest moving blocks in any equity market.

Consumer discretionary companies sell things that can be postponed, which is why LVMH, Hermès International, Kering, Nike Inc. and Home Depot Inc. are read against consumer confidence and disposable income. Consumer staples sell things that cannot, which is why Procter and Gamble, Nestlé SA, Unilever plc, Coca-Cola Co. and PepsiCo Inc. are conventionally described as defensive. Utilities and real estate both carry heavy long dated debt and distribute steady cash, so Iberdrola, Enel SpA, National Grid, Emaar Properties and Aldar Properties are among the most rate sensitive listings in any market. Health care spans a defensive pharmaceutical base and a far more volatile development pipeline, which is why AstraZeneca, Novartis AG and Roche Holding behave differently from a single trial result company.

The cyclical and defensive division 

The oldest division across the sectors is between the cyclical groups, whose revenue tracks the economic cycle, and the defensive groups, whose revenue does not vary much with it. Energy, materials, industrials, financials and consumer discretionary sit on the cyclical side. Consumer staples, utilities and much of health care sit on the defensive side. The division is descriptive: a defensive company is not one whose share price cannot fall, only one whose sales do not fall as far when demand weakens.

Sector rotation is the name given to the observation that money appears to move between these groups as expectations about growth and rates change, and it is one of the oldest conventions in equity commentary. It is worth stating its limits plainly. Rotation is identified after the fact, from returns that are already known. The classifications it uses are reassigned periodically. The sensitivities it rests on are not stable, because a company's debt, its customers and its input mix all change. And the same sector can be described as cyclical or defensive depending on which part of it is being pointed at. It describes what a set of returns did; it is not a mechanism that produces the next set.

Why grouped shares move as a block 

Three separate mechanisms produce the same appearance. The first is genuine shared exposure: one input price, one customer, one regulator, one interest rate. The second is inference. When one company in a group reports, the market reprices its peers immediately on the assumption that the same conditions applied to them, which is why a semiconductor result moves every semiconductor listing before any of the others has said a word. The third is mechanical: sector exchange traded funds and sector allocations inside larger funds buy and sell every constituent in proportion to its weight, so a flow into the sector lifts the whole group regardless of any individual company's news.

The consequence for anything held across several shares is that a count of positions is not a measure of spread. Five positions in one sector share one sensitivity, and a single sector level event reaches all five at once with the same sign.

Where the label stops describing the company 

A sector label is assigned on revenue, and revenue is not the only thing that determines how a share trades. A retailer that has built a large advertising business, a car manufacturer whose value has come to rest on software expectations, and a bank whose earnings are dominated by a payments division are all filed under a label that describes their past better than their present. The clearest recurring case is the group of very large platform companies, which have been reassigned between technology, communication services and consumer discretionary as the schemes have been redrawn, without their businesses changing at all.

Two further caveats matter. Sector groups are not equally sized, so a sector level statistic is dominated by its largest constituents and can move on one company. And correlation within a sector is not constant: it rises sharply when the market moves as a whole and falls when attention returns to individual results, which means a measurement taken in one regime describes the other badly.