The following commentary comes from an independent investor or market observer as part of TheStreet's guest contributor program, which is separate from the company's news coverage.

NEW YORK ( ETF Expert) -- Scores of investment gurus live on momentum and relative strength. They may advocate investing solely in those assets that have put together streaks over four, eight and 12 weeks.

Other media darlings don't care what happens in a shorter period. They may run with a particular theme for decades. For instance, Jim Rogers likes commodities and the China growth story, despite the bumps that may occur along the path.

Sometimes, the hottest three-month winners are the same investments that fit a longer-term premise. For example, in 2009 as well as in parts of 2010, commodities and commodity-rich nations benefited from U.S. government decisions that weakened the U.S. dollar. Those that believe in the dollar's demise over the long-term profited in shorter-term periods as well as year-over-year periods.

Some longer-term themes fall on deaf ears. The notion of cheap P/Es and an aging baby boomer demographic didn't help healthcare-related stocks in 2009 or 2010; healthcare-related stocks severely underperformed in year-over-year periods as well as longer-term time frames.

Interestingly enough, health care has rocketed year to date . Pharma ETFs and Biotech ETFs even look pretty sharp over the last 12 weeks, showing tremendous relative strength.

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