Relative strength (RS) measures how a security performs relative to a benchmark or peer group rather than in absolute terms — typically a stock versus its index, or a sector versus the broad market. The core idea behind rotation is to lean toward whatever is currently leading (and away from what's lagging), on the premise that leadership persists long enough to be tradeable. This is a section-overview node: it defines the family and routes to three child nodes — Relative Strength vs the Index (single name vs SPX/SPY), Sector Relative Strength (groups vs the market and vs each other), and RS Line & New Highs (the ratio line as a chart overlay and the "RS new high before price" signal). The central tension is that RS is one of the best-supported ideas in the technical toolkit, yet the way most discretionary traders apply it is far weaker than the evidence behind it.

What it is, and what it is not

"Relative strength" is overloaded — keep two unrelated things apart:

• Relative strength / relative momentum (this section): cross-sectional outperformance — this asset vs that asset. Computed as a price ratio (stock ÷ benchmark) or a percentile rank (e.g. IBD's RS Rating, 1–99). This is the family with academic support.
• RSI — the Relative Strength Index (Wilder, a different node): a bounded 0–100 oscillator of an asset's own up/down moves. Despite the shared word, it has nothing to do with relative momentum and does not inherit its evidence. Conflating them is the single most common error here.

How it's measured

The workhorse is the price relative (ratio) line: divide the security's price by the benchmark's price over time and plot it. A rising line = outperformance, falling = underperformance — independent of whether the absolute price is up or down (StockCharts ChartSchool). Common forms:

• Ratio line / RS line — e.g. stock ÷ SPY (or ÷ S&P 500), often the chart overlay O'Neil/IBD popularized.
• Percentile RS Rating — rank of trailing (often ~12-month) return vs a universe; IBD scales 1–99 and flags ≥80–90 as leadership.
• Relative-momentum portfolios — the academic construction: rank the universe by trailing 3–12-month return, go long top decile / short bottom decile, rebalance monthly.

How it's used in practice

Filter and rotate, not time. Traders screen for names whose RS line is rising or making new highs and against laggards; rotate exposure toward leading sectors/industries; and use the RS line as a confirmation overlay — bullish when RS makes a new high at or before price does (often before a breakout). Sector-level rotation is the institutional version (overweight leading groups, underweight laggards). Operational specifics — exact ranks, lookbacks, entries/stops — live in the child nodes and the Swing Trading branch.

Standing & evidence — an honest positive meta-take

This is one of the few TA-adjacent concepts with strong, robust academic support, so the section is unusually well-founded:

• Single-stock momentum: Jegadeesh & Titman (1993) showed buying past 3–12-month winners and selling past losers earned significant positive returns across every formation/holding combination they tested; the effect has since replicated across decades, markets, and asset classes.
• Industry/sector momentum: Moskowitz & Grinblatt (1999) found a strong industry-momentum effect that accounts for much of individual-stock momentum — directly underwriting sector rotation.

That support is real and should be respected. But four caveats keep it from being a blank check:

1. Portfolio ≠ single trade. The documented edge is for diversified, long/short, rules-based, monthly-rebalanced portfolios (top vs bottom decile of hundreds of names). It does not transfer 1:1 to a concentrated, discretionary single-name trade — that's an out-of-sample bet, not the studied effect. 2. Momentum crashes. Momentum returns are negatively skewed with rare but severe drawdowns (Daniel & Moskowitz, 2016, document historical monthly losses cited up to ~90%), concentrated in post-bear "panic" rebounds. Chasing leaders works until it violently doesn't. 3. Not RSI. The evidence belongs to relative/cross-sectional momentum, not the weakly-supported RSI oscillator. Don't let the shared name transfer credibility. 4. Cycle-rotation folklore. "Which sector leads which phase of the economic cycle" (the Sector Rotation Model) is intuitive but soft — the timing of which group leads when is closer to narrative than to the measured momentum edge. Treat it as a lens, not a signal.

Strengths & limitations

• Strengths: measured, persistent, broad cross-asset support; conceptually simple; the ratio line is hard to fool (it's just relative price).
• Limitations: crash risk and regime dependence (worst right after major bottoms); whipsaw in choppy/mean-reverting tapes; lookback-sensitive (short windows = noise, long = stale); benchmark choice changes the read; and the gap between portfolio evidence and single-name application.
• #1 misuse: treating a high RS rating as a standalone buy on one stock and assuming the J-T edge carries over — it's a relative ranking, not a portfolio's expected return.

Child nodes

• Relative Strength vs the Index — one name vs SPX/SPY; ratio line and RS rating mechanics.
• Sector Relative Strength — groups vs market and vs each other; the rotation construction with the strongest evidence.
• RS Line & New Highs — the overlay and the "RS new high before price breakout" signal (O'Neil/IBD).

System relevance

Relative-strength inputs feed the Augustus trade-setup agent as leadership/context signals, paired with sector-level RS for regime alignment. Hard caveat for downstream consumers: RS is portfolio-grade evidence applied to single names — Augustus must size for momentum-crash skew and not treat a high RS rank as a standalone entry. Whether a given RS read translates to a profitable trade is Augustus's call with live data + Cairn's measured record, not this doc's.

Sources

• Jegadeesh, N. & Titman, S. (1993), "Returns to Buying Winners and Selling Losers," Journal of Finance 48(1):65–91 — onlinelibrary.wiley.com / bauer.uh.edu reprint.
• Moskowitz, T. & Grinblatt, M. (1999), "Do Industries Explain Momentum?" Journal of Finance 54(4):1249–1290 — onlinelibrary.wiley.com; aqr.com.
• Daniel, K. & Moskowitz, T. (2016), "Momentum Crashes," Journal of Financial Economics 122:221–247 — nber.org/papers/w20439.
• StockCharts ChartSchool — "Price Relative / Relative Strength" (ratio-line mechanics).
• Investor's Business Daily / O'Neil — RS Rating and RS Line in CAN SLIM (RS line at new high before breakout).