The difference here is that when two questions become linked (also a crowdsourced action - as everything is), the results of the precedent question can become the major weight of the dependent question in a sub-level way.
As an illustration:
Top question of "Is global warming something that people should change their energy habits on?"
Precedent question that arises "Is man's CO2 production great enough to shift the overall balance?"
And that one might have two precedents of "How much does it take to shift the overall balance?"
And "How much CO2 is man producing?"
So as the results of the precedent questions get fleshed out, they affect the higher level questions. As people investigate them, the trend towards those being more important and choose to weigh them higher. As this process continues, the direct results of the original question and the opinions carry less and less weight. So the net effect is that the two most root questions actually answer the one above.
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