RCKSX vs. VIIIX

Last updated Jun 4, 2026

RCKSX (Rock Oak Core Growth Fund) and VIIIX (Vanguard Institutional Index Fund Institutional Plus Shares) are both mutual funds - RCKSX is a Large Cap Blend Equities fund managed by Oak Associates, while VIIIX is a S&P 500 fund tracking the S&P 500 Index. Over the past 10 years, RCKSX returned 10.85%/yr vs 15.74%/yr for VIIIX. Their correlation of 0.87 suggests significant overlap in exposure. RCKSX charges 1.25%/yr vs 0.02%/yr for VIIIX.

Performance

RCKSX vs. VIIIX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in Rock Oak Core Growth Fund (RCKSX) and Vanguard Institutional Index Fund Institutional Plus Shares (VIIIX). The values are adjusted to include any dividend payments, if applicable.

Returns By Period

In the year-to-date period, RCKSX achieves a 14.10% return, which is significantly higher than VIIIX's 11.70% return. Over the past 10 years, RCKSX has underperformed VIIIX with an annualized return of 10.85%, while VIIIX has yielded a comparatively higher 15.74% annualized return.

RCKSX

• 1D: -0.13%
• 1M: 1.87%
• YTD: 14.10%
• 6M: 14.42%
• 1Y: 20.18%
• 3Y*: 19.62%
• 5Y*: 7.42%
• 10Y*: 10.85%

VIIIX

• 1D: 0.13%
• 1M: 5.80%
• YTD: 11.70%
• 6M: 11.74%
• 1Y: 28.99%
• 3Y*: 23.17%
• 5Y*: 14.42%
• 10Y*: 15.74%

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

RCKSX vs. VIIIX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019	2018	2017
RCKSX Rock Oak Core Growth Fund	14.10%	12.99%	15.12%	15.57%	-18.09%	9.96%	13.75%	19.05%	-2.14%	22.69%
VIIIX Vanguard Institutional Index Fund Institutional Plus Shares	11.70%	17.87%	26.29%	25.79%	-18.14%	28.69%	18.41%	31.48%	-4.41%	21.82%

Correlation

The correlation between RCKSX and VIIIX is 0.63, which is moderate. They share some common price drivers but move independently often enough to provide real diversification benefit when combined.

	Correlation
Correlation (1Y) Calculated over the trailing 1-year period	0.63
Correlation (3Y) Calculated over the trailing 3-year period	0.71
Correlation (5Y) Calculated over the trailing 5-year period	0.81
Correlation (10Y) Calculated over the trailing 10-year period	0.84
Correlation (All Time) Calculated using the full available price history since Jan 4, 2005	0.87

Over the past year, the correlation between RCKSX and VIIIX has dropped to 0.63 - well below their long-term average of 0.87, suggesting their price drivers have been diverging.

Return for Risk

RCKSX vs. VIIIX — Risk / Return Rank

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

RCKSX

RCKSX Risk / Return Rank: 56
RCKSX Sharpe Ratio Rank: 39
RCKSX Sortino Ratio Rank: 40
RCKSX Omega Ratio Rank: 34
RCKSX Calmar Ratio Rank: 93
RCKSX Martin Ratio Rank: 75

VIIIX

VIIIX Risk / Return Rank: 73
VIIIX Sharpe Ratio Rank: 76
VIIIX Sortino Ratio Rank: 67
VIIIX Omega Ratio Rank: 67
VIIIX Calmar Ratio Rank: 74
VIIIX 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.

RCKSX vs. VIIIX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for Rock Oak Core Growth Fund (RCKSX) and Vanguard Institutional Index Fund Institutional Plus Shares (VIIIX). 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.

	RCKSX	VIIIX	Difference
Sharpe ratio: Return per unit of total volatility	1.83	2.52	-0.69
Sortino ratio: Return per unit of downside risk	2.66	3.42	-0.77
Omega ratio: Gain probability vs. loss probability	1.31	1.46	-0.15
Calmar ratio: Return relative to maximum drawdown	5.11	3.36	+1.75
Martin ratio: Return relative to average drawdown	14.18	15.69	-1.51
Data is calculated on a 1-year rolling basis and updated daily. The trend shows the change in the indicator over the past month.

RCKSX vs. VIIIX - Sharpe Ratio Comparison

The current RCKSX Sharpe Ratio is 1.83, which is comparable to the VIIIX Sharpe Ratio of 2.52. The chart below compares the historical Sharpe Ratios of RCKSX and VIIIX, 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

	RCKSX	VIIIX	Difference
Sharpe Ratio (1Y) Calculated over the trailing 1-year period	1.83	2.52	-0.69
Sharpe Ratio (5Y) Calculated over the trailing 5-year period	0.48	0.86	-0.38
Sharpe Ratio (10Y) Calculated over the trailing 10-year period	0.62	0.87	-0.25
Sharpe Ratio (All Time) Calculated using the full available price history	0.38	0.50	-0.12

Drawdowns

RCKSX vs. VIIIX - Drawdown Comparison

The maximum RCKSX drawdown since its inception was -57.88%, roughly equal to the maximum VIIIX drawdown of -55.18%. Use the drawdown chart below to compare losses from any high point for RCKSX and VIIIX.

Drawdown Indicators

	RCKSX	VIIIX	Difference
Max Drawdown Largest peak-to-trough decline	-57.88%	-55.18%	-2.70%
Max Drawdown (1Y) Largest decline over 1 year	-4.14%	-8.90%	+4.76%
Max Drawdown (3Y) Largest decline over 3 years	-18.22%	-18.75%	+0.53%
Max Drawdown (5Y) Largest decline over 5 years	-22.54%	-24.50%	+1.96%
Max Drawdown (10Y) Largest decline over 10 years	-33.10%	-33.79%	+0.69%
Current Drawdown Current decline from peak	-0.60%	0.00%	-0.60%
Average Drawdown Average peak-to-trough decline	-9.51%	-10.02%	+0.51%
Ulcer Index Depth and duration of drawdowns from previous peaks	1.49%	1.90%	-0.41%

Volatility

RCKSX vs. VIIIX - Volatility Comparison

Rock Oak Core Growth Fund (RCKSX) and Vanguard Institutional Index Fund Institutional Plus Shares (VIIIX) have volatilities of 2.94% and 2.83%, respectively, indicating that both stocks experience similar levels of price fluctuations. This suggests that the risk associated with both stocks, as measured by volatility, is nearly the same. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	RCKSX	VIIIX	Difference
Volatility (1M) Calculated over the trailing 1-month period	2.94%	2.83%	+0.11%
Volatility (6M) Calculated over the trailing 6-month period	8.06%	8.97%	-0.91%
Volatility (1Y) Calculated over the trailing 1-year period	11.56%	11.86%	-0.30%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	15.66%	16.89%	-1.23%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	17.55%	18.06%	-0.51%

RCKSX vs. VIIIX - Expense Ratio Comparison

RCKSX has a 1.25% expense ratio, which is higher than VIIIX's 0.02% expense ratio.

Dividends

RCKSX vs. VIIIX - Dividend Comparison

RCKSX's dividend yield for the trailing twelve months is around 5.48%, more than VIIIX's 2.41% yield.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
RCKSX Rock Oak Core Growth Fund	5.48%	6.26%	0.47%	0.71%	1.00%	4.31%	16.56%	3.18%	0.59%	5.91%	0.70%	3.21%
VIIIX Vanguard Institutional Index Fund Institutional Plus Shares	2.41%	2.11%	3.66%	2.66%	3.39%	4.79%	3.07%	2.86%	2.45%	1.84%	2.38%	2.47%

Frequently Asked Questions

Can I hold both RCKSX and VIIIX in my portfolio?

RCKSX and VIIIX have a correlation of 0.63, meaning they provide meaningful diversification benefit when combined. Depending on your allocation goals, holding both could reduce overall portfolio risk.

Which is riskier, RCKSX or VIIIX?

RCKSX has higher volatility (2.94%) compared to VIIIX (2.83%). In terms of maximum drawdown, RCKSX dropped -57.88% vs VIIIX's -55.18%.

Which has better risk-adjusted returns?

VIIIX currently has the higher Sharpe Ratio (2.52 vs 1.83), 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.