Stocks course · Section 4: Charts, Indicators and Strategies
Sector Rotation and Correlation: How Stock Sectors Move Together
The 11 stock market sectors, what correlation means and why it decides real diversification, and how sector rotation strategies work with examples.
Intermediate5 min read·6:30 video·Lesson 17 of 26·quiz: 4 questions
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Stocks are grouped into sectors, such as information technology, energy and health care, and stocks in the same sector tend to move together because the same forces drive their profits. Correlation measures how closely two investments move, from -1 (opposite) to +1 (in step), and sector rotation is the idea of shifting money between sectors as the economy and market leadership change. Understanding both helps you avoid portfolios that look diversified but are really one bet, and helps you judge rotation strategies realistically.
The 11 sectors
The most widely used scheme is the Global Industry Classification Standard (GICS), which sorts companies into 11 sectors:
| Sector | Examples of businesses | Usual character |
|---|---|---|
| Information Technology | Chips, software, hardware | Cyclical, growth |
| Communication Services | Internet platforms, media, telecoms | Mixed |
| Consumer Discretionary | Cars, online retail, hotels, restaurants | Cyclical |
| Consumer Staples | Food, drinks, household goods | Defensive |
| Health Care | Drug makers, medical devices, insurers | Defensive |
| Financials | Banks, insurers, payment companies | Cyclical, rate-sensitive |
| Industrials | Aerospace, machinery, transport | Cyclical |
| Energy | Oil and gas producers and services | Cyclical, tied to oil prices |
| Materials | Chemicals, metals, mining | Cyclical |
| Utilities | Electricity, gas, water | Defensive, rate-sensitive |
| Real Estate | Property trusts (REITs) | Rate-sensitive |
The scheme is revised from time to time; for example, payment processors were moved from technology to financials in 2023. Check the current classification on a fund's or index provider's website.
Cyclical sectors earn much more in booms and much less in recessions. Defensive sectors sell things people buy in any economy, so their profits are steadier.
Correlation in plain terms
- +1: always moved in the same direction in step.
- 0: no consistent relationship.
- -1: always moved in opposite directions.
Two oil producers might have a correlation of +0.8 or more. An oil producer and a software company will usually be lower. Correlation is measured on past returns, it changes over time and it says nothing about cause.
Why correlation decides real diversification
Example
You split money 50/50 between two stocks, each with yearly volatility (a measure of how much returns swing) of 30%. Portfolio volatility depends on their correlation:
- Correlation +0.9 (two chipmakers): about 29%, barely better than one stock.
- Correlation +0.2 (a chipmaker and a food company): about 23%.
- Correlation 0: about 21%.
The formula is the square root of (0.5² x 0.3² + 0.5² x 0.3² + 2 x 0.5 x 0.5 x correlation x 0.3 x 0.3).
Holding ten technology stocks is closer to one bet than ten. Real diversification comes from owning businesses driven by different things (see diversification and portfolio construction).
Risk
Correlations between stocks tend to rise in market crashes, when investors sell almost everything at once. In the sharp falls of 2008 and early 2020, most sectors dropped together. Diversifying across stocks reduces the risk of one company failing, but it cannot remove the risk of the whole market falling.
Business-cycle sector rotation
The classic map links sectors to phases of the economy:
| Phase | Sectors that have often led |
|---|---|
| Early recovery (rates low, growth picking up) | Financials, consumer discretionary, industrials |
| Mid-cycle (steady growth) | Technology, industrials, communication services |
| Late cycle (inflation and rates rising) | Energy, materials |
| Recession | Consumer staples, utilities, health care |
Treat this as a rough map, not a timetable. Real cycles are messy, and markets usually move months before the economic data confirms a turn, so by the time a recession is official, defensive sectors may already have had their run. Interest rates and inflation also cut across the map: in 2022, when inflation and rates jumped, energy stocks rose strongly while many technology stocks fell sharply.
Relative-strength rotation: a testable version
Instead of forecasting the economy, a relative-strength rotation follows what the market is already doing. It is momentum (see stock trading strategies) applied to sectors.
Example
At the end of each month you rank the 11 sector funds by their 12-month return and hold the top three in equal amounts. This month energy (+24%), industrials (+18%) and financials (+15%) lead, so you hold those. Next month technology climbs into the top three and financials drops out, so you sell financials and buy technology. With $9,000, each fund gets about $3,000.
This can keep you in leading sectors and out of collapsing ones, but it suffers when leadership flips quickly (sharp rebounds) and it concentrates you in a few sectors at once. Test it with costs before using it.
Practical habits
- Know your sector exposure. Add up your holdings by sector. If one sector is more than about a third of your portfolio, be sure it is deliberate.
- Know your index exposure. Broad market-cap indices are now heavy in a few large technology-related companies, so "owning the market" already carries a big sector bet.
- Watch correlations when adding a stock. A new holding that behaves like what you already own adds risk without much diversification.
- Do not confuse a sector rally with skill. If all your picks rose, check whether their sector simply rose.
Tip
Open the DanioX stocks market page, take the 20 largest companies and write each one's sector next to it. You will see how much of the top of the US market sits in a few sectors, which is useful context before you build a "diversified" portfolio.
This completes the analysis sections. Next you move to the most important skill in trading: position sizing and stop-losses.
Key takeaways
- Stocks are grouped into 11 sectors, and stocks in the same sector usually move together.
- Correlation runs from -1 to +1; combining assets with low correlation lowers portfolio swings.
- Correlations between stocks tend to rise in market crashes, just when diversification is needed most.
- Business-cycle rotation is a useful map but hard to time; relative-strength rotation is a testable form of momentum.
Quiz: check what you learned
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⚠ Not financial advice — educational signals only. Read the disclaimer.