MDY vs SGI: Correlation
Measured on weekly returns over the past three years, SPDR S&P MidCap 400 ETF (MDY) and Somnigroup International Inc. (SGI) carry a correlation of 0.68, a strong link.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are MDY and SGI?
Over the past 3 years, MDY and SGI moved with a correlation of 0.68, which is strong. Recent behaviour matches the longer record: 0.63 over 1 year against 0.68 over 3. Over 5 years the correlation is 0.69, and the annualized covariance of weekly returns is 380.9 %².
By 3-year correlation, SGI places #85 of the 359 assets tracked against MDY. Correlation aside, the last 12 months split them widely, with MDY ahead by 43.7 points (+18.3% versus -25.4%). Note the risk asymmetry: SGI runs 2.0 times the annualized volatility of the other leg, so equal-weighting the two is not an equal-risk position.
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 SGI: side by side
| MDY (SPDR S&P MidCap 400 ETF) | SGI (Somnigroup International Inc.) | |
|---|---|---|
| 1-year return | +18.3% | -25.4% |
| 5-year return | +47.5% | +44.9% |
| Volatility (ann.) | 16.5% | 33.8% |
| Beta vs S&P 500 | 0.91 | 1.02 |
| Max drawdown (3Y) | -24.0% | -37.1% |
| Market cap | – | $13.1B |
| P/E (trailing) | – | 24.8 |
| Dividend yield | 1.02% | 1.02% |
| Expense ratio | 0.23% | – |
| Assets under management | $26.5B | – |
| Sector / category | ETF · US Small & Mid Cap | US Listed |
MDY is a Mid-Cap Blend fund from State Street Investment Management: $26.5B under management, 400 holdings, a 0.23% expense ratio, a 1.02% trailing dividend yield.
Year-by-year returns
| Year | MDY | SGI |
|---|---|---|
| 2022 | -13.3% | -26.0% |
| 2023 | +16.1% | +50.1% |
| 2024 | +13.6% | +12.3% |
| 2025 | +7.2% | +58.8% |
| 2026 | +16.4% | -29.5% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Fund exposure
Keep in mind that MDY holds SGI at a 0.36% weight, which makes a slice of this correlation mechanical rather than coincidental.
Are MDY and SGI good diversifiers for each other?
Somewhat, no more. With 0.68 correlation, most large moves hit both names, and the diversification benefit stays modest.
FAQ
What is the correlation between MDY and SGI?
The MDY/SGI correlation stands at 0.68 on a 3-year window (1 year: 0.63, 5 years: 0.69), computed from weekly returns as of 2026-08-27.
Is SGI a good diversifier for MDY?
Somewhat, no more. With 0.68 correlation, most large moves hit both names, and the diversification benefit stays modest.
What does a correlation of 0.68 mean?
A reading of 0.68 sits on a scale from −1 (opposite moves) through 0 (unrelated) to +1 (identical moves). Correlation captures direction, not magnitude or performance.
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Related comparisons
Hubs: MDY correlations · SGI correlations
