Health care stocks are among the riskiest games investors can play these days. The reason, of course, is the health care reform effort, spearheaded by President Barack Obama and winding its way through Congress.

What makes this confusing is that reform could significantly help or hurt particular industries within health care -- depending on how the law is written.

BusinessWeek's Aaron Pressman discussed the debate over hospital stocks in this video.

Stifel Nicolaus (SF) recently issued a 63-page report analyzing the possible effect of health care reform on various health care stocks. A few of the key conclusions:

First, the bullish case for health care stocks is easy to understand: Health care reform could boost overall health care spending by bringing 48-million uninsured people onto insurance rolls. Stifel cites the Commonwealth Fund, which estimates a 16% increase in the insured could result in an extra $122 billion in spending each year.

But, second, Stifel analysts question this thesis, seeing an increased risk to firms' profits from health care reform. The political tone has changed because of worries about mounting deficits, "suggest[ing] that more aggressive cost cutting and increased regulation may result." That's a change from May, when health care stocks actually outperformed the market on better-than-expected earnings and hopes of positive effects from reform.

Finally, Stifel's experts warn this debate could take a long time:

Health reform legislation is likely to take most of 2009 to finalize and will continue to be a headline risk for most healthcare sectors throughout the process.

Some health care industries are less exposed to the debate -- "medical and drug distributors, generic pharmaceuticals and possibly large-cap pharmaceutical and biotechnology companies." But for most of the health care sector -- and for its investors -- this could be a long, volatile year.