MDY vs PII: Correlation
How closely do SPDR S&P MidCap 400 ETF (MDY) and Polaris Inc. (PII) trade together? Their weekly returns over three years give a correlation of 0.60, which is strong.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are MDY and PII?
Over the past 3 years, MDY and PII moved with a correlation of 0.60, which is strong. Little has changed lately, as the 1-year reading of 0.64 lands near the 3-year figure. Over 5 years the correlation is 0.62, and the annualized covariance of weekly returns is 384.0 %².
By 3-year correlation, PII places #181 of the 359 assets tracked against MDY. Their 12-month results are close: +18.3% for MDY against +15.8% for PII. Risk is not evenly split, since PII 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 PII: side by side
| MDY (SPDR S&P MidCap 400 ETF) | PII (Polaris Inc.) | |
|---|---|---|
| 1-year return | +18.3% | +15.8% |
| 5-year return | +47.5% | -39.0% |
| Volatility (ann.) | 16.5% | 39.0% |
| Beta vs S&P 500 | 0.91 | 1.07 |
| Max drawdown (3Y) | -24.0% | -70.4% |
| Market cap | – | $3.6B |
| P/E (trailing) | – | – |
| Dividend yield | 1.02% | 4.24% |
| 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 | PII |
|---|---|---|
| 2022 | -13.3% | -6.0% |
| 2023 | +16.1% | -3.8% |
| 2024 | +13.6% | -37.2% |
| 2025 | +7.2% | +15.9% |
| 2026 | +16.4% | +3.1% |
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 PII at a 0.09% weight, which makes a slice of this correlation mechanical rather than coincidental.
Are MDY and PII good diversifiers for each other?
To a limited degree. At 0.60 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 PII?
The MDY/PII correlation stands at 0.60 on a 3-year window (1 year: 0.64, 5 years: 0.62), computed from weekly returns as of 2026-08-27.
Is PII a good diversifier for MDY?
To a limited degree. At 0.60 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 0.60 mean?
A reading of 0.60 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-pii.json
Embed this badge (it refreshes with the data), with attribution:
[](https://www.pairbook.io/pair/mdy-vs-pii/)
No key needed, free to use. Full endpoint list in the API documentation.
Related comparisons
Hubs: MDY correlations · PII correlations
