David Vomund, president of Vomund Investment Management, released his second book on ETFs this year: Exchange Traded Profits: Cashing In on New ETF Trading Methods.

In it, the Incline Village, Nev.-based registered investment adviser explains how you can, while spending only a few minutes every two weeks, invest like a pro using a few simple trading strategies that have beaten the market.

Vomund, who manages $12 million in assets, talked with IBD about how his investment models work:

IBD: What is your most profitable trading strategy and how do you carry it out?

Vomund: My favored model is a mechanical relative-strength model used to buy the best-performing ETFs. To calculate relative strength, we look at each ETF’s performance over the last six months and then place a higher weight on the most recent price activity.

The formula breaks the past 120 business days into quarters (four 30-day periods). We run a percentage change calculation on each 30-day quarter, and then average the percentage changes, placing twice the weight on the most recent quarter. I post rankings of ETFs by their relative strength each weekend at www.ETFtradingstrategies.com.

Every other Friday, you buy the two best-performing ETFs based on the relative strength calculation. If your current holdings are outperforming (in the top half of the report) then you continue to hold them. If not, you sell them and buy the best performers.

This model has three variations using style index ETFs, sector ETFs and market segment ETFs. The style-index model uses seven style index ETFs including iShares S&P 500 Large-Cap Value (ARCA:IVE ), PowerShares QQQ (NASDAQ:QQQ ), SPDR S&P 500 (ARCA:SPY ), SPDR S&P MidCap 400 (ARCA:MDY ), iShares S&P SmallCap Value (ARCA:IJS ), iShares S&P SmallCap Growth (ARCA:IJT ) and iShares Russell 2000 Index (ARCA:IWM ).

Also included is iShares Barclays 20+ Year U.S. Treasury Bonds (ARCA:TLT ) to add safety in a bad market.

Between 1998 and Sept. 16, 2011, this model returned 9.61% on average annually vs. 1.65% for the S&P 500, excluding dividends. There are seven round-trip trades with an average holding period of 101 days.

The market segment model uses QQQ, SPY, TLT along with PowerShares DB Commodity Index (ARCA:DBC ), PowerShares DB U.S. Dollar Index Bearish (ARCA:UDN ), and ProShares Short S&P 500 (ARCA:SH ).

Since 1998 it has a 15.76% average annual return with an average holding period of 118 days.

Most of these ETFs don’t date back to 1998 so in these cases we bought gold and the index they track. In the case of SH, we created our own index, which moves opposite to the S&P 500.