MFRFX vs. SSSYX

Last updated Jun 4, 2026

MFRFX (MFS Research Fund) and SSSYX (State Street Equity 500 Index Fund Class K) are both Large Cap Blend Equities funds. Over the past 10 years, MFRFX returned 13.14%/yr vs 15.61%/yr for SSSYX. With a 0.97 correlation, they move nearly in lockstep. MFRFX charges 0.78%/yr vs 0.02%/yr for SSSYX.

Performance

MFRFX vs. SSSYX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in MFS Research Fund (MFRFX) and State Street Equity 500 Index Fund Class K (SSSYX). The values are adjusted to include any dividend payments, if applicable.

Returns By Period

In the year-to-date period, MFRFX achieves a 7.13% return, which is significantly lower than SSSYX's 11.69% return. Over the past 10 years, MFRFX has underperformed SSSYX with an annualized return of 13.14%, while SSSYX has yielded a comparatively higher 15.61% annualized return.

MFRFX

• 1D: -0.05%
• 1M: 3.78%
• YTD: 7.13%
• 6M: 7.31%
• 1Y: 19.90%
• 3Y*: 17.25%
• 5Y*: 10.15%
• 10Y*: 13.14%

SSSYX

• 1D: 0.14%
• 1M: 5.79%
• YTD: 11.69%
• 6M: 11.73%
• 1Y: 28.94%
• 3Y*: 22.73%
• 5Y*: 14.24%
• 10Y*: 15.61%

*Multi-year figures are annualized to reflect compound growth (CAGR)

MFRFX vs. SSSYX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019	2018	2017
MFRFX MFS Research Fund	7.13%	12.80%	18.77%	22.49%	-17.21%	24.66%	16.63%	33.13%	-4.51%	23.31%
SSSYX State Street Equity 500 Index Fund Class K	11.69%	17.81%	24.99%	26.27%	-18.16%	28.51%	18.31%	31.38%	-4.38%	21.61%

Correlation

The correlation between MFRFX and SSSYX is 0.97 - these two move nearly in lockstep. At this level, holding both provides almost no diversification benefit. If you already own one, adding the other does little to reduce portfolio risk.

	Correlation
Correlation (1Y) Calculated over the trailing 1-year period	0.97
Correlation (3Y) Calculated over the trailing 3-year period	0.98
Correlation (5Y) Calculated over the trailing 5-year period	0.98
Correlation (10Y) Calculated over the trailing 10-year period	0.97
Correlation (All Time) Calculated using the full available price history since Sep 19, 2014	0.97

The correlation between MFRFX and SSSYX has been stable across timeframes, ranging from 0.97 to 0.98 - a consistent structural relationship.

Return for Risk

MFRFX vs. SSSYX — Risk / Return Rank

Compare risk-adjusted metric ranks to identify better-performing investments over the past 12 months.

MFRFX

MFRFX Risk / Return Rank: 37
MFRFX Sharpe Ratio Rank: 37
MFRFX Sortino Ratio Rank: 35
MFRFX Omega Ratio Rank: 37
MFRFX Calmar Ratio Rank: 33
MFRFX Martin Ratio Rank: 44

SSSYX

SSSYX Risk / Return Rank: 73
SSSYX Sharpe Ratio Rank: 75
SSSYX Sortino Ratio Rank: 67
SSSYX Omega Ratio Rank: 67
SSSYX Calmar Ratio Rank: 74
SSSYX Martin Ratio Rank: 83

The rank (0–100) shows how this investment's returns compare to the risk taken. Higher = better. Based on the past 12 months of data, combining Sharpe, Sortino, and other metrics used by quantitative funds and institutional investors.

MFRFX vs. SSSYX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for MFS Research Fund (MFRFX) and State Street Equity 500 Index Fund Class K (SSSYX). Risk-adjusted metrics are performance indicators that assess an investment's returns in relation to its risk, enabling a more accurate comparison of different investment options.

	MFRFX	SSSYX	Difference
Sharpe ratio: Return per unit of total volatility	1.77	2.52	-0.75
Sortino ratio: Return per unit of downside risk	2.46	3.42	-0.96
Omega ratio: Gain probability vs. loss probability	1.32	1.46	-0.13
Calmar ratio: Return relative to maximum drawdown	2.14	3.36	-1.21
Martin ratio: Return relative to average drawdown	9.26	15.69	-6.42
Data is calculated on a 1-year rolling basis and updated daily. The trend shows the change in the indicator over the past month.

MFRFX vs. SSSYX - Sharpe Ratio Comparison

The current MFRFX Sharpe Ratio is 1.77, which is comparable to the SSSYX Sharpe Ratio of 2.52. The chart below compares the historical Sharpe Ratios of MFRFX and SSSYX, calculated using daily returns over the previous 12 months. A higher Sharpe Ratio indicates better risk-adjusted performance relative to the risk-free rate.

Sharpe Ratios by Period

	MFRFX	SSSYX	Difference
Sharpe Ratio (1Y) Calculated over the trailing 1-year period	1.77	2.52	-0.75
Sharpe Ratio (5Y) Calculated over the trailing 5-year period	0.62	0.85	-0.23
Sharpe Ratio (10Y) Calculated over the trailing 10-year period	0.75	0.13	+0.62
Sharpe Ratio (All Time) Calculated using the full available price history	0.44	0.12	+0.32

Drawdowns

MFRFX vs. SSSYX - Drawdown Comparison

The maximum MFRFX drawdown since its inception was -56.15%, smaller than the maximum SSSYX drawdown of -91.48%. Use the drawdown chart below to compare losses from any high point for MFRFX and SSSYX.

Drawdown Indicators

	MFRFX	SSSYX	Difference
Max Drawdown Largest peak-to-trough decline	-56.15%	-91.48%	+35.33%
Max Drawdown (1Y) Largest decline over 1 year	-9.63%	-8.88%	-0.75%
Max Drawdown (3Y) Largest decline over 3 years	-19.19%	-18.74%	-0.45%
Max Drawdown (5Y) Largest decline over 5 years	-23.37%	-24.49%	+1.12%
Max Drawdown (10Y) Largest decline over 10 years	-33.52%	-91.48%	+57.96%
Current Drawdown Current decline from peak	-0.05%	0.00%	-0.05%
Average Drawdown Average peak-to-trough decline	-14.45%	-4.15%	-10.30%
Ulcer Index Depth and duration of drawdowns from previous peaks	2.22%	1.90%	+0.32%

Volatility

MFRFX vs. SSSYX - Volatility Comparison

The current volatility for MFS Research Fund (MFRFX) is 2.58%, while State Street Equity 500 Index Fund Class K (SSSYX) has a volatility of 2.82%. This indicates that MFRFX experiences smaller price fluctuations and is considered to be less risky than SSSYX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	MFRFX	SSSYX	Difference
Volatility (1M) Calculated over the trailing 1-month period	2.58%	2.82%	-0.24%
Volatility (6M) Calculated over the trailing 6-month period	8.91%	8.96%	-0.05%
Volatility (1Y) Calculated over the trailing 1-year period	11.69%	11.85%	-0.16%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	16.56%	16.88%	-0.32%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	17.60%	124.46%	-106.86%

MFRFX vs. SSSYX - Expense Ratio Comparison

MFRFX has a 0.78% expense ratio, which is higher than SSSYX's 0.02% expense ratio.

Dividends

MFRFX vs. SSSYX - Dividend Comparison

MFRFX's dividend yield for the trailing twelve months is around 15.02%, more than SSSYX's 1.29% yield.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
MFRFX MFS Research Fund	15.02%	16.09%	10.04%	6.68%	7.56%	5.43%	5.09%	3.68%	12.52%	8.80%	4.63%	6.98%
SSSYX State Street Equity 500 Index Fund Class K	1.29%	1.44%	1.63%	1.78%	2.16%	2.76%	1.86%	4.44%	5.18%	5.94%	2.07%	1.84%

Frequently Asked Questions

Can I hold both MFRFX and SSSYX in my portfolio?

With a correlation of 0.97, MFRFX and SSSYX move almost identically. Holding both adds very little diversification - you're essentially doubling your position in the same market segment. Choosing one is usually more capital-efficient.

Which is riskier, MFRFX or SSSYX?

SSSYX has higher volatility (2.82%) compared to MFRFX (2.58%). In terms of maximum drawdown, MFRFX dropped -56.15% vs SSSYX's -91.48%.

Which has better risk-adjusted returns?

SSSYX currently has the higher Sharpe Ratio (2.52 vs 1.77), meaning it's delivered slightly more return per unit of risk over the trailing 12 months. However, this ranking shifts over time - use the Risk/Return Score above for a more comprehensive view that combines Sharpe, Sortino, and other measures used by quantitative funds.