Currently considered are all, year, 3-month, and month.
Topic on Talk:Wikistats 2.0 Design Project/RequestforFeedback/Round1/Detail page single wiki
All time is really needed. Would be great to have an adjustable range (e.g. I want to see development of Ukrainian Wikisource from 2006 to 2008 only)
I would add to the ones provided: 6 months.
Wikistats page views uses 24 months. I'd say 24,36,48 or even 60 months instead of 12 months helps greatly to not draw wrong conclusions from growth or decline where these are essentially (partially) random fluctuations. Easy to check at https://stats.wikimedia.org/EN/TablesPageViewsMonthlyCombined.htm Imagine only last 12 months were shown. In many cases trend would seem consistently up or down where wider scope shows this is not the case at all.