MDY vs OSIS: Correlation
SPDR S&P MidCap 400 ETF (MDY) and OSI Systems, Inc. (OSIS) 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 OSIS?
On 3 years of weekly data the MDY/OSIS correlation comes out at 0.62, strong. The relationship has been stable: the 1-year correlation (0.55) sits close to the 3-year figure. The 5-year figure is 0.58, and annualized covariance runs at 386.9 %².
By 3-year correlation, OSIS places #153 of the 359 assets tracked against MDY. Correlation aside, the last 12 months split them widely, with MDY ahead by 26.8 points (+18.3% versus -8.5%). Risk is not evenly split, since OSIS carries 2.3 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 OSIS: side by side
| MDY (SPDR S&P MidCap 400 ETF) | OSIS (OSI Systems, Inc.) | |
|---|---|---|
| 1-year return | +18.3% | -8.5% |
| 5-year return | +47.5% | +113.6% |
| Volatility (ann.) | 16.5% | 38.1% |
| Beta vs S&P 500 | 0.91 | 1.39 |
| Max drawdown (3Y) | -24.0% | -36.2% |
| Market cap | – | $3.4B |
| P/E (trailing) | – | 23.6 |
| Dividend yield | 1.02% | 0.00% |
| 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 | OSIS |
|---|---|---|
| 2022 | -13.3% | -14.7% |
| 2023 | +16.1% | +62.3% |
| 2024 | +13.6% | +29.7% |
| 2025 | +7.2% | +52.3% |
| 2026 | +16.4% | -17.3% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Are MDY and OSIS good diversifiers for each other?
Somewhat, no more. With 0.62 correlation, most large moves hit both names, and the diversification benefit stays modest.
FAQ
What is the correlation between MDY and OSIS?
As of 2026-08-27, the correlation of weekly returns between MDY and OSIS is 0.62 over 3 years, 0.55 over 1 year and 0.58 over 5 years.
Is OSIS a good diversifier for MDY?
Somewhat, no more. With 0.62 correlation, most large moves hit both names, and the diversification benefit stays modest.
What does a correlation of 0.62 mean?
On the −1 to +1 scale, 0.62 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-osis.json
Drop this badge in a README or notebook; it updates with the data:
[](https://www.pairbook.io/pair/mdy-vs-osis/)
The core API is free. Terms and every endpoint in the API documentation.
Related comparisons
Hubs: MDY correlations · OSIS correlations
