MDY vs ROCK: Correlation
Measured on weekly returns over the past three years, SPDR S&P MidCap 400 ETF (MDY) and Gibraltar Industries, Inc. (ROCK) carry a correlation of 0.64, a strong link.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are MDY and ROCK?
Over the past 3 years, MDY and ROCK moved with a correlation of 0.64, which is strong. Little has changed lately, as the 1-year reading of 0.59 lands near the 3-year figure. Over 5 years the correlation is 0.65, and the annualized covariance of weekly returns is 413.1 %².
Among the 359 assets we track against MDY, ROCK ranks #128 by 3-year correlation. Their recent paths diverged sharply: over the last 12 months MDY outperformed by 47.3 percentage points (+18.3% for MDY against -29.0% for ROCK). Risk is not evenly split, since ROCK carries 2.4 times the volatility of the other side.
How is this computed?
Pearson correlation on weekly returns: ρ(A,B) = cov(rA, rB) / (σA · σB), over windows of 52, 156 and 260 weeks. Covariance is annualized (×52) and expressed in %². Full definitions on the methodology page.
MDY vs ROCK: side by side
| MDY (SPDR S&P MidCap 400 ETF) | ROCK (Gibraltar Industries, Inc.) | |
|---|---|---|
| 1-year return | +18.3% | -29.0% |
| 5-year return | +47.5% | -39.2% |
| Volatility (ann.) | 16.5% | 39.2% |
| Beta vs S&P 500 | 0.91 | 1.19 |
| Max drawdown (3Y) | -24.0% | -61.2% |
| Market cap | – | $1.4B |
| P/E (trailing) | – | 22.9 |
| Dividend yield | 1.02% | 0.00% |
| Expense ratio | 0.23% | – |
| Assets under management | $26.5B | – |
| Sector / category | ETF · US Small & Mid Cap | US Listed |
On the fund side, MDY sits in the Mid-Cap Blend category at State Street Investment Management, with $26.5B under management, 400 holdings, a 0.23% expense ratio, a 1.02% trailing dividend yield.
Year-by-year returns
| Year | MDY | ROCK |
|---|---|---|
| 2022 | -13.3% | -31.2% |
| 2023 | +16.1% | +72.1% |
| 2024 | +13.6% | -25.4% |
| 2025 | +7.2% | -16.1% |
| 2026 | +16.4% | -7.3% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Are MDY and ROCK good diversifiers for each other?
Only partially. A correlation of 0.64 means MDY and ROCK share most of their swings. Pairing them dampens volatility somewhat, but it will not protect against a common drawdown.
FAQ
What is the correlation between MDY and ROCK?
As of 2026-08-27, the correlation of weekly returns between MDY and ROCK is 0.64 over 3 years, 0.59 over 1 year and 0.65 over 5 years.
Is ROCK a good diversifier for MDY?
Only partially. A correlation of 0.64 means MDY and ROCK share most of their swings. Pairing them dampens volatility somewhat, but it will not protect against a common drawdown.
What does a correlation of 0.64 mean?
On the −1 to +1 scale, 0.64 describes how much the two returns move together: +1 is lockstep, 0 is independence, negative values mean opposite directions. It says nothing about which performed better.
Use this data
$ curl https://www.pairbook.io/api/v1/pairs/mdy-vs-rock.json
Markdown for the live badge, attribution link included:
[](https://www.pairbook.io/pair/mdy-vs-rock/)
Free with attribution; caching and terms are described in the API documentation.
Related comparisons
Hubs: MDY correlations · ROCK correlations
