Change in Sub-Domains Linking to Sub-Domain
This alert monitors the normalized (logarithmically-scaled) sum of all external sub-domains linking link to a sub-domain of the source URL (Moz Documentation). Changes in MozRank can be associated with the change in the number of sub-domains linking to your sub-domain. Hypertext links are generally associated with an increase or decrease in the amount of authority passed to your website internally.
Increase in External Sub-Domains Linking to Sub-Domain
An increase in your MozRank has the potential to indicate you have received additional external sub-domains linking to your website that are passing authority to the Sub-Domain. This is a good indicator that your site is earning valuable authority, and will contribute to higher rankings.
Decrease in External Sub-Domains Linking to your Sub-Domain
If the external sub-domain links pointing to your sub-domain are decreasing, that typically indicates you are losing domain authority. If you see this number dropping, you should check your site for a recent drop in backlinks to your site. Consistent drops in MozRank from a loss of authoritative links to your root domain can be an early indicator of lost rankings.
Let’s hope you have recently garnered new authoritative external links to your sub-domain, and that you see this number on a steady upward trend. It is important to note that Moz can trigger false positives for this alert if there was a recent index update on their end, which would have an impact on the MozRank of all sites in their index. If you see a big jump or drop, you should check to see if Moz updated their index before freaking out!