If you click the above graphic from FinViz, you'll see an elegant display of sector strength (which sectors show more green than red), but also where individual stocks within each of the sectors fall in terms of performance. Some very interesting ideas for pairs trades could come from such a look. Monitoring the graphic over time could also help traders see situations in which the market as a whole strengthens, or--in today's case--reverses and weakens. What you would see is both which sectors lead the market movement and which stocks within those sectors are acting as leaders.
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