Stocks and bonds are the two foundational asset classes of investment portfolios, and the relationship between them is the central axis of intermarket analysis. A stock is an ownership claim on a company's residual cash flows; a bond is a creditor claim entitled to fixed interest and return of principal. That structural difference drives everything downstream — bonds sit senior in the capital structure (paid before equity in bankruptcy), carry lower and more predictable returns, and are less volatile, while equities offer open-ended upside in exchange for full exposure to the downside. The core tension for the practitioner is not which is "better" but how the two move relative to each other: whether they hedge each other (negative correlation) or fall together (positive correlation) is regime-dependent, and that single fact governs portfolio diversification, the 60/40 model, and the intermarket reads that feed macro positioning.

The structural differences

Bondholders rank ahead of stockholders in liquidation and usually recover something; equity holders are last and often recover nothing (CFI; PIMCO). The trade-off is that equities have historically delivered a positive equity risk premium over government bonds. Dimson, Marsh & Staunton's multi-country, ~106-year dataset reports a realized world equity premium over bonds of roughly 4% (the premium over bills is higher, ~4.7%); more importantly, they infer a forward-looking expected premium of only about 3–3.5% geometric / 4.5–5% arithmetic — lower than older U.S.-only estimates and, they argue, still likely generous (DMS 2006). Damodaran's working estimates have ranged ~4–5.5% depending on method and period (Damodaran). These are long-horizon averages, not numbers any single year respects.

The correlation relationship — the heart of it

For intermarket purposes the decisive variable is the stock–bond correlation, and it is time-varying, not fixed. Measured correlations have swung across a wide band — academic work spanning the 1980s–2020s reports a range from roughly −0.6 to +0.5 depending on the window (Andersson et al.; Vanguard). Two broad regimes recur:

• Negative correlation ("flight to quality" regime). When the dominant shock is to growth — recession fears, demand collapse, risk-off panic — money flees stocks into the safety of government bonds. Stocks fall, bond prices rise. Here bonds hedge equities; this is the regime the 60/40 portfolio is built for. Murphy frames this as the deflationary case, where stocks and bonds move inversely.
• Positive correlation ("inflation/rates" regime). When the dominant shock is to inflation or discount rates — a hawkish central bank, an inflation surprise — both asset classes are repriced by the same rising-rate force and fall together. Murphy frames the "normal" inflationary environment as positively correlated. 2022 is the textbook case: as the Fed tightened aggressively, the S&P 500 and the Bloomberg Aggregate fell together and their correlation spiked to roughly +0.5, the highest in the sample (AQR; Vanguard; Morningstar).

The historical sequence matters: U.S. Treasuries had a positive beta to stocks through the 1980s–90s, then the correlation flipped negative in the late 1990s across most G7 markets and stayed broadly negative from ~2000 to ~2021 (monthly correlation around −0.2), before the 2022 inflation shock pushed it sharply positive (ScienceDirect; AQR). The driver consensus: the inflation regime sets the sign — high/volatile inflation pushes correlation positive; stable, low inflation keeps it negative (AQR; Morningstar; Yang/Zhou/Wang for the 150-year view).

How it's used in practice

1. Portfolio diversification (the 60/40). The entire rationale of holding bonds alongside stocks is the expectation of negative correlation — bonds cushion equity drawdowns. This works in flight-to-quality regimes and fails in inflation regimes; 2022 (both legs down) is the canonical breakdown, and the practical lesson is that the diversification benefit is conditional, not structural (Vanguard; AQR). 2. Intermarket / business-cycle reads. In Murphy's framework, bonds, stocks, and commodities rotate in a recognizable sequence around the business cycle; bonds often turn before stocks at cycle tops. Practitioners watch bond yields (and the yield curve) as a leading macro input for equities (StockCharts ChartSchool). 3. Relative valuation — the "Fed model." Compares the equity forward earnings yield to the 10-year Treasury yield, treating stocks as "cheap vs bonds" when the earnings yield exceeds the bond yield. It is widely cited but theoretically contested (see below). 4. Risk-on / risk-off gauge. The direction of the relationship is itself a sentiment read: bonds bid + stocks sold = risk-off; the reverse = risk-on.

Standing & evidence

The structural facts (seniority, the existence of an equity risk premium) are uncontested. The correlation is well-documented as real but unstable — this is settled in the academic literature, with the regime-switching behavior tied to inflation, real rates, and the nature of the shock (AQR; ScienceDirect; the 150-year study of Yang et al.). The Fed model is the genuinely disputed piece: Asness ("Fight the Fed Model," 2003) shows it commits an inflation illusion by equating a real earnings yield to a nominal bond yield, and Bekaert & Engstrom find the comovement is largely explained by inflation co-moving with both — not by stocks being mispriced relative to bonds. The model fit the U.S. mainly in 1921–1928 and 1987–2000 and travels poorly across countries (Wikipedia/Fed model; Asness; Bekaert & Engstrom). Treat the Fed model as a heuristic, not a valuation truth.

Strengths & limitations

• Works when: the regime is stable and identified. In a low-inflation, growth-shock-dominated world, the negative correlation is dependable and bonds genuinely hedge equities.
• Fails when: inflation/rate shocks dominate. Then stocks and bonds fall together, diversification evaporates, and any "bonds will save the portfolio" assumption is dangerous — exactly the 2022 outcome.
• #1 misuse: treating the stock–bond correlation (or the 60/40 diversification benefit) as a constant. It is regime-conditional and can flip sign within a single year. A second common error is using the Fed model as a precise fair-value tool rather than a rough sentiment heuristic.

System relevance

This node anchors the Intermarket Analysis branch and pairs with its siblings (Stocks vs Commodities, Stocks vs FX, Bond Yields). For Delvantic's regime engine, the stock–bond correlation sign is a primary regime classifier — the same input that tells the Augustus trade-setup agent whether the macro backdrop is flight-to-quality (bond-hedged) or inflation-driven (correlated-down) risk. Hard caveat for any consumer: the correlation is time-varying and inflation-conditional; never hard-code a sign or assume bonds hedge equities without checking the current regime.

Sources

• Corporate Finance Institute — Bonds vs Stocks: Overview, Pros/Cons (seniority, claim type)
• PIMCO — Bonds 101: Comparing Stocks and Bonds
• Dimson, Marsh & Staunton — The Worldwide Equity Premium: A Smaller Puzzle (SSRN, 2006)
• Aswath Damodaran — Estimating Equity Risk Premiums (NYU Stern)
• AQR — A Changing Stock-Bond Correlation; Asness — Fight the Fed Model (JPM, 2003)
• Vanguard — The stock/bond correlation: increasing amid inflation
• Morningstar — What Higher Inflation Means for Stock/Bond Correlations
• ScienceDirect — Stock-bond return correlation: understanding the changing behaviour; Yang, Zhou & Wang — Stock–bond correlation and macroeconomic conditions: 150 years of evidence
• StockCharts ChartSchool — Intermarket Analysis; John Murphy — Intermarket Analysis: Profiting from Global Market Relationships
• Bekaert & Engstrom — Inflation and the Stock Market: Understanding the "Fed Model"; Wikipedia — Fed model

Dispute flagged: the Fed model's validity is genuinely contested (Asness, Bekaert/Engstrom vs. its practitioner users). Long-run equity-risk-premium figures vary materially by source and method.