MDY vs MSM: Correlation
SPDR S&P MidCap 400 ETF (MDY) and MSC Industrial Direct Company, Inc. (MSM) show a strong relationship: their 3-year correlation of weekly returns is 0.62.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are MDY and MSM?
Over the past 3 years, MDY and MSM moved with a correlation of 0.62, which is strong. The link has loosened recently: the 1-year correlation (0.51) runs below the 3-year figure (0.62). Over 5 years the correlation is 0.66, and the annualized covariance of weekly returns is 260.8 %².
Within MDY's tracked universe of 359 assets, MSM comes in at #152 by 3-year correlation. Correlation aside, the last 12 months split them widely, with MSM ahead by 19.8 points (+18.3% versus +38.1%). One caveat on sizing: MSM is 1.5 times as volatile as the other leg, so an equal-dollar split is far from equal-risk.
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 MSM: side by side
| MDY (SPDR S&P MidCap 400 ETF) | MSM (MSC Industrial Direct Company, Inc.) | |
|---|---|---|
| 1-year return | +18.3% | +38.1% |
| 5-year return | +47.5% | +73.8% |
| Volatility (ann.) | 16.5% | 25.3% |
| Beta vs S&P 500 | 0.91 | 0.78 |
| Max drawdown (3Y) | -24.0% | -29.3% |
| Market cap | – | – |
| P/E (trailing) | – | 29.6 |
| Dividend yield | 1.02% | 2.84% |
| 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 | MSM |
|---|---|---|
| 2022 | -13.3% | +0.9% |
| 2023 | +16.1% | +28.5% |
| 2024 | +13.6% | -23.4% |
| 2025 | +7.2% | +17.4% |
| 2026 | +16.4% | +49.1% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Fund exposure
A structural note: 0.15% of MDY is MSM itself, so the fund partly moves with the stock by construction.
Are MDY and MSM good diversifiers for each other?
To a limited degree. At 0.62 the two still catch most of the same waves, so the pair smooths returns a little without insulating either from a shared selloff.
FAQ
What is the correlation between MDY and MSM?
The MDY/MSM correlation stands at 0.62 on a 3-year window (1 year: 0.51, 5 years: 0.66), computed from weekly returns as of 2026-08-27.
Is MSM a good diversifier for MDY?
To a limited degree. At 0.62 the two still catch most of the same waves, so the pair smooths returns a little without insulating either from a shared selloff.
What does a correlation of 0.62 mean?
Correlation ranges from −1 to +1. Values near +1 mean two assets move together, near 0 that they move independently, and negative values that they tend to move in opposite directions. It measures co-movement, not performance.
Use this data
$ curl https://www.pairbook.io/api/v1/pairs/mdy-vs-msm.json
Markdown for the live badge, attribution link included:
[](https://www.pairbook.io/pair/mdy-vs-msm/)
The core API is free. Terms and every endpoint in the API documentation.
Related comparisons
Hubs: MDY correlations · MSM correlations
