MDY vs ULBI: Correlation
How closely do SPDR S&P MidCap 400 ETF (MDY) and Ultralife Corporation (ULBI) trade together? Their weekly returns over three years give a correlation of 0.47, which is moderate.
Data as of 2026-08-27 · refreshed every trading day · weekly returns · methodology
How correlated are MDY and ULBI?
Across a 3-year window, the weekly returns of MDY and ULBI correlate at 0.47, moderate. Recent behaviour matches the longer record: 0.40 over 1 year against 0.47 over 3. Stretching to 5 years gives 0.30, with an annualized covariance of 460.4 %².
Among the 359 assets we track against MDY, ULBI ranks #325 by 3-year correlation. Their recent paths diverged sharply: over the last 12 months MDY outperformed by 24.0 percentage points (+18.3% for MDY against -5.7% for ULBI). Note the risk asymmetry: ULBI runs 3.6 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 ULBI: side by side
| MDY (SPDR S&P MidCap 400 ETF) | ULBI (Ultralife Corporation) | |
|---|---|---|
| 1-year return | +18.3% | -5.7% |
| 5-year return | +47.5% | -19.1% |
| Volatility (ann.) | 16.5% | 59.1% |
| Beta vs S&P 500 | 0.91 | 1.74 |
| Max drawdown (3Y) | -24.0% | -68.8% |
| Market cap | – | $0.1B |
| P/E (trailing) | – | – |
| 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 | ULBI |
|---|---|---|
| 2022 | -13.3% | -36.1% |
| 2023 | +16.1% | +76.7% |
| 2024 | +13.6% | +9.2% |
| 2025 | +7.2% | -23.2% |
| 2026 | +16.4% | +13.8% |
Calendar-year price returns; the current year is year-to-date as of the data date above.
Are MDY and ULBI good diversifiers for each other?
Reasonably. At 0.47, MDY and ULBI keep a meaningful degree of independence, and combining them has historically reduced portfolio volatility.
FAQ
What is the correlation between MDY and ULBI?
The MDY/ULBI correlation stands at 0.47 on a 3-year window (1 year: 0.40, 5 years: 0.30), computed from weekly returns as of 2026-08-27.
Is ULBI a good diversifier for MDY?
Reasonably. At 0.47, MDY and ULBI keep a meaningful degree of independence, and combining them has historically reduced portfolio volatility.
What does a correlation of 0.47 mean?
On the −1 to +1 scale, 0.47 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-ulbi.json
Drop this badge in a README or notebook; it updates with the data:
[](https://www.pairbook.io/pair/mdy-vs-ulbi/)
Free with attribution; caching and terms are described in the API documentation.
Related comparisons
Hubs: MDY correlations · ULBI correlations
