Why is Month the only period base for Period Changes analysis?

[pover]

Why is the Month (not sure if it's referring to a field or master item) only period base? It doesn't appear to change the analysis because I've defined calendar periods and I can select the periods once I add Month. The funny part is that I'm not using Month as the base field in any of those calendar periods. 

Does anyone have any insight into this behavior?

[Nasser_Bumpus]

Interesting. I've gone into a sample app of mine and was able to switch between Month, Quarter, and Year. Have you defined these calendar periods in Business Logic? It would look like this :