OBSOX vs. VIIIX

Last updated Jun 24, 2026

OBSOX (Oberweis Small-Cap Opportunities Fund) and VIIIX (Vanguard Institutional Index Fund Institutional Plus Shares) are both mutual funds - OBSOX is a Small Cap Growth Equities fund managed by Oberweis, while VIIIX is a S&P 500 fund tracking the S&P 500 Index. Over the past 10 years, OBSOX returned 19.88%/yr vs 15.87%/yr for VIIIX. A 0.79 correlation means they provide meaningful diversification when combined. OBSOX charges 1.25%/yr vs 0.02%/yr for VIIIX.

Performance

OBSOX vs. VIIIX - Performance Comparison

The chart below illustrates the hypothetical performance of a $10,000 investment in Oberweis Small-Cap Opportunities Fund (OBSOX) 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, OBSOX achieves a 42.09% return, which is significantly higher than VIIIX's 9.78% return. Over the past 10 years, OBSOX has outperformed VIIIX with an annualized return of 19.88%, while VIIIX has yielded a comparatively lower 15.87% annualized return.

OBSOX

• 1D: 1.65%
• 1M: 8.07%
• YTD: 42.09%
• 6M: 38.71%
• 1Y: 64.25%
• 3Y*: 25.72%
• 5Y*: 17.41%
• 10Y*: 19.88%

VIIIX

• 1D: -0.37%
• 1M: 0.10%
• YTD: 9.78%
• 6M: 8.78%
• 1Y: 25.51%
• 3Y*: 21.80%
• 5Y*: 13.75%
• 10Y*: 15.87%

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

OBSOX vs. VIIIX - Yearly Performance Comparison

	2026 (YTD)	2025	2024	2023	2022	2021	2020	2019	2018	2017
OBSOX Oberweis Small-Cap Opportunities Fund	42.09%	14.28%	16.13%	15.81%	-11.17%	43.39%	32.52%	25.06%	-7.05%	25.55%
VIIIX Vanguard Institutional Index Fund Institutional Plus Shares	9.78%	17.87%	26.29%	25.79%	-18.14%	28.69%	18.41%	31.48%	-4.41%	21.82%

Correlation

The correlation between OBSOX and VIIIX is 0.75, 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	0.75
Correlation (3Y) Calculated over the trailing 3-year period	0.79
Correlation (5Y) Calculated over the trailing 5-year period	0.82
Correlation (10Y) Calculated over the trailing 10-year period	0.81
Correlation (All Time) Calculated using the full available price history since Jul 7, 1997	0.79

The correlation between OBSOX and VIIIX has been stable across timeframes, ranging from 0.75 to 0.82 - a consistent structural relationship.

Return for Risk

OBSOX vs. VIIIX — Risk / Return Rank

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

OBSOX

OBSOX Risk / Return Rank: 81
OBSOX Sharpe Ratio Rank: 83
OBSOX Sortino Ratio Rank: 68
OBSOX Omega Ratio Rank: 63
OBSOX Calmar Ratio Rank: 96
OBSOX Martin Ratio Rank: 96

VIIIX

VIIIX Risk / Return Rank: 65
VIIIX Sharpe Ratio Rank: 64
VIIIX Sortino Ratio Rank: 57
VIIIX Omega Ratio Rank: 59
VIIIX Calmar Ratio Rank: 68
VIIIX Martin Ratio Rank: 78

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.

OBSOX vs. VIIIX - Risk-Adjusted Trends Comparison

This table presents a comparison of risk-adjusted performance metrics for Oberweis Small-Cap Opportunities Fund (OBSOX) 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.

Values are calculated on a 1-year rolling basis and updated daily. Risk-adjusted metrics are more stable over longer periods — use the period switch above to explore them.

	OBSOX	VIIIX	Difference
Sharpe ratio: Return per unit of total volatility	2.50	2.15	+0.35
Sortino ratio: Return per unit of downside risk	3.13	2.91	+0.22
Omega ratio: Gain probability vs. loss probability	1.40	1.39	+0.01
Calmar ratio: Return relative to maximum drawdown	5.84	3.02	+2.82
Martin ratio: Return relative to average drawdown	21.31	13.62	+7.68

OBSOX vs. VIIIX - Sharpe Ratio Comparison

The current OBSOX Sharpe Ratio is 2.50, which is comparable to the VIIIX Sharpe Ratio of 2.15. The chart below compares the historical Sharpe Ratios of OBSOX 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.

Drawdowns

OBSOX vs. VIIIX - Drawdown Comparison

The maximum OBSOX drawdown since its inception was -80.52%, which is greater than VIIIX's maximum drawdown of -55.18%. Use the drawdown chart below to compare losses from any high point for OBSOX and VIIIX.

Drawdown Indicators

	OBSOX	VIIIX	Difference
Max Drawdown Largest peak-to-trough decline	-80.52%	-55.18%	-25.34%
Max Drawdown (1Y) Largest decline over 1 year	-11.40%	-8.90%	-2.50%
Max Drawdown (3Y) Largest decline over 3 years	-27.74%	-18.75%	-8.99%
Max Drawdown (5Y) Largest decline over 5 years	-28.65%	-24.50%	-4.15%
Max Drawdown (10Y) Largest decline over 10 years	-42.79%	-33.79%	-9.00%
Current Drawdown Current decline from peak	0.00%	-1.72%	+1.72%
Average Drawdown Average peak-to-trough decline	-30.50%	-10.00%	-20.50%
Ulcer Index Depth and duration of drawdowns from previous peaks	3.11%	1.97%	+1.14%

Volatility

OBSOX vs. VIIIX - Volatility Comparison

Oberweis Small-Cap Opportunities Fund (OBSOX) has a higher volatility of 9.31% compared to Vanguard Institutional Index Fund Institutional Plus Shares (VIIIX) at 4.68%. This indicates that OBSOX's price experiences larger fluctuations and is considered to be riskier than VIIIX based on this measure. The chart below showcases a comparison of their rolling one-month volatility.

Volatility by Period

	OBSOX	VIIIX	Difference
Volatility (1M) Calculated over the trailing 1-month period	9.31%	4.68%	+4.63%
Volatility (6M) Calculated over the trailing 6-month period	21.60%	9.84%	+11.76%
Volatility (1Y) Calculated over the trailing 1-year period	26.68%	12.50%	+14.18%
Volatility (5Y) Calculated over the trailing 5-year period, annualized	25.28%	16.98%	+8.30%
Volatility (10Y) Calculated over the trailing 10-year period, annualized	24.89%	18.11%	+6.78%

OBSOX vs. VIIIX - Expense Ratio Comparison

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

Dividends

OBSOX vs. VIIIX - Dividend Comparison

OBSOX has not paid dividends to shareholders, while VIIIX's dividend yield for the trailing twelve months is around 2.45%.

Position	TTM	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015
OBSOX Oberweis Small-Cap Opportunities Fund	0.00%	0.00%	0.80%	0.00%	0.17%	21.88%	4.05%	3.04%	28.22%	6.36%	4.24%	11.91%
VIIIX Vanguard Institutional Index Fund Institutional Plus Shares	2.45%	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 OBSOX and VIIIX in my portfolio?

OBSOX and VIIIX have a correlation of 0.75, meaning they provide meaningful diversification benefit when combined. Depending on your allocation goals, holding both could reduce overall portfolio risk.

Which is riskier, OBSOX or VIIIX?

OBSOX has higher volatility (9.31%) compared to VIIIX (4.68%). In terms of maximum drawdown, OBSOX dropped -80.52% vs VIIIX's -55.18%.

Which has better risk-adjusted returns?

OBSOX currently has the higher Sharpe Ratio (2.50 vs 2.15), 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.