The count of the external links is an insufficient datum in her even, because she does not allow to distinguish the really influencing sites of the sites which bring almost no visit.

The only way to measure the contribution is to analyze the audience's datas of the site towards which the external links point. All the services or stats tools parse "referrers" or URL of origin which correspond to Web pages having brought a guest by the bais of a hypertext link.

For classifications on Google, potential of a site as influencer can be partially obtained by observing its Page Rank through the Google Toolbar or specialized web sites. This is however an indication among the others on the value of this site, because it is necessary to consider also the number of links proposed by this site and the context of these links.
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