The deep link ratio is the ratio of external inbound links to pages other than your home page. We compare all the inbound links we can find that go to your home page and compare this with links that go to other pages within your site.
For effective SEO, you really need a higher number of topically relevant quality links from trusted sites to pages deep within your site.
The more high quality backlinks from relevant sites, the higher your site will rank. Backlinks to your interior pages (deep links) are more valuable for SEO as they are more likely to point to content that web searchers are looking for. The more links pointing to your interior pages, the higher your SEO Deep Link Ratio. This is simply the number of deep links divided by the total number backlinks. It’s useful to see how you compare to your competitors on this front and whether other sites are finding your content more useful than your competition.