Dear Jamie Brock,
I had the same question a few days before. Now, found the answer.
When you write a new hub, the starting score of the new hub is given as 50. So the average score of the whole hubs will go a little bit down, until the new hub is viewed and gets more score.
Let us say, you have 9 hubs and their average is 70, then when you write your new 10th hub, the average score will become 68 and gradually increases when the new hub starts working successfully getting more scores.
Hope this helps.