MDY vs WMS: Correlation
Measured on weekly returns over the past three years, SPDR S&P MidCap 400 ETF (MDY) and Advanced Drainage Systems, Inc. (WMS) carry a correlation of 0.66, a strong link.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are MDY and WMS?
Over the past 3 years, MDY and WMS moved with a correlation of 0.66, which is strong. The link has tightened recently: the 1-year correlation (0.77) runs above the 3-year figure (0.66). Over 5 years the correlation is 0.63, and the annualized covariance of weekly returns is 401.6 %².
Within MDY's tracked universe of 359 assets, WMS comes in at #105 by 3-year correlation. Correlation aside, the last 12 months split them widely, with MDY ahead by 22.7 points (+18.3% versus -4.4%). Note the risk asymmetry: WMS runs 2.2 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 WMS: side by side
| MDY (SPDR S&P MidCap 400 ETF) | WMS (Advanced Drainage Systems, Inc.) | |
|---|---|---|
| 1-year return | +18.3% | -4.4% |
| 5-year return | +47.5% | +22.1% |
| Volatility (ann.) | 16.5% | 37.1% |
| Beta vs S&P 500 | 0.91 | 1.31 |
| Max drawdown (3Y) | -24.0% | -45.8% |
| Market cap | – | $10.5B |
| P/E (trailing) | – | 23.6 |
| Dividend yield | 1.02% | 0.52% |
| Expense ratio | 0.23% | – |
| Assets under management | $26.5B | – |
| Sector / category | ETF · US Small & Mid Cap | US Listed |
MDY, State Street Investment Management's Mid-Cap Blend fund, carries $26.5B under management, 400 holdings, a 0.23% expense ratio, a 1.02% trailing dividend yield.
Year-by-year returns
| Year | MDY | WMS |
|---|---|---|
| 2022 | -13.3% | -39.5% |
| 2023 | +16.1% | +72.4% |
| 2024 | +13.6% | -17.5% |
| 2025 | +7.2% | +26.0% |
| 2026 | +16.4% | -3.9% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Fund exposure
WMS represents 0.28% of MDY's portfolio, so part of any move in MDY is WMS itself, and the correlation between them is partly mechanical.
Are MDY and WMS good diversifiers for each other?
Somewhat, no more. With 0.66 correlation, most large moves hit both names, and the diversification benefit stays modest.
FAQ
What is the correlation between MDY and WMS?
As of 2026-08-27, the correlation of weekly returns between MDY and WMS is 0.66 over 3 years, 0.77 over 1 year and 0.63 over 5 years.
Is WMS a good diversifier for MDY?
Somewhat, no more. With 0.66 correlation, most large moves hit both names, and the diversification benefit stays modest.
What does a correlation of 0.66 mean?
A reading of 0.66 sits on a scale from −1 (opposite moves) through 0 (unrelated) to +1 (identical moves). Correlation captures direction, not magnitude or performance.
Use this data
$ curl https://www.pairbook.io/api/v1/pairs/mdy-vs-wms.json
Drop this badge in a README or notebook; it updates with the data:
[](https://www.pairbook.io/pair/mdy-vs-wms/)
The core API is free. Terms and every endpoint in the API documentation.
Related comparisons
Hubs: MDY correlations · WMS correlations
