Low-volatility strategies have long been a go-to strategy for individual investors, institutional investors and especially retirees. The thought process behind the low-volatility strategy is that high-quality stocks that are the least volatile will outperform volatile stocks over the long term. High-quality stocks are generally the big-name corporations with stable earnings, healthy dividends and strong balance sheets. While volatility is not always negative, it can certainly cause headaches and emotional distress, particularly to retirement investors who are searching for stability and reliable returns.

The boom in exchange-traded funds (ETFs) has created a whole new category of products geared towards low-volatility strategies, which have gained popularity over the past couple of years. It is possible for investors to gain exposure to low-volatility equities across the world, which can help diversify portfolios and improve risk within portfolios. These three low-volatility ETFs provide diversification and lower volatility risk exposure to the markets as the seventh anniversary of the bull market approaches.

iShares MSCI All Country World Mini Vol

The iShares MSCI All Country World Mini Vol ETF (NYSEARCA: ACWV) is one of the top low-volatility ETFs out there for diversification. This ETF allows investors to gain exposure to low-volatility stocks from across the world. The ETF charges a reasonable expense ratio of 0.2% and yields 2.28%. Performance has been very strong for this ETF, which has not seen a losing year since 2012, the first full year of its existence.

The majority of the ETF's holdings are in giant-and large-cap stocks at 35.4 and 43.66%, respectively. Health care makes up the largest sector exposure at 17.18% of the portfolio, followed by consumer defensive at 16.79% and financial services at 12.32%. While this ETF does have exposure around the world, the portfolio is underweight in European equities and emerging markets. About 64.25% of the portfolio is invested in North and South America, followed by 27.41% exposure to Asia, and only 8.34% exposure to Europe. Overall, the portfolio is allocated 93.89% in developed countries and only 6.11% in emerging markets.

PowerShares S&P Em Mkts Low Volatil ETF

Emerging markets may not be the latest fad or the most popular strategy on Wall Street right now, as commodities continue to tumble and China sends shock waves around the world, but that is where low volatility comes in. The emerging markets are certainly more sensitive to world economic conditions, which have been cloudy to start 2016, to say the least.

However, investors searching for diversification or a small exposure to emerging markets should take a look at the PowerShares S&P Em Mkts Low Volatil ETF (NYSEARCA: EELV). The ETF currently has an expense ratio of 0.29% and sports a yield of 2.5%. Its performance was lousy in 2015, which is to be expected with the global uncertainty and Chinese market meltdown in the latter half of 2015.

Turning to portfolio makeup, 45.85% of the portfolio is allocated to large-cap stocks and 28.94% is allocated to giant-cap stocks, making up the two largest market caps in the portfolio. Financial services stocks have a 32.65% allocation, while 12.38% is in consumer defensive and 9.87% is in communication services. Despite being called as an emerging market ETF, the portfolio does have almost 30% exposure to developed markets as well, which should further help tame volatility.

O'Shares FTSE Europe Quality Div ETF

A newcomer to the ETF space is O'Shares Investments, which has famed "Shark Tank" investor Kevin O'Leary as chairman of the company. O'Shares separates itself from the herd by focusing on low volatility stocks of high quality that also happen to pay strong dividends.

Investors could take a look the O'Shares FTSE Europe Quality Div ETF (NYSEARCA: OEUR) for exposure to European equities. The ETF only began trading in August 2015, so there is not a whole lot of past performance information available. However, the ETF comes after O'Leary's many years of success running O'Leary Funds and various other investments, as seen on the "Shark Tank" TV show. Investors who are familiar with O'Leary and his disciplined investment style may be more inclined to shrug off the age of this ETF.

The ETF has an expense ratio of 0.58%, pays a monthly dividend and has seen returns of -7.39% since its inception in August 2015. A vast majority of the ETF is allocated to giant-cap stocks, at 65.84% of the portfolio, followed by large-cap stocks at 26.56% and mid-cap stocks at 7.59%. The three largest sector allocations for this ETF are consumer defensive at 19.11%, followed by health care at 17.1% and energy at 11.73%.