Changing Source column for formula depending on month

Hi guys

So I've nearly finished my document, this last bit is killing me. I've attached what i've done so far, and tried to highlight where my problem is.

Basically, I have this formula in my summary page:

=SUM(SUMIF(Attendance!$I:$I,{"Y","A"},Attendance!$D:$D))

In the Attendance sheet in the formula, column $I:$I refers to October. In the summary page, it currently shows the data for October. What I want to be able to do, is for the user to use the picklist in the Summary page to change the month, which therefore changes the column that the formula references (for example, if they change the picklist to 'November' then the new formula should reference column J):

=SUM(SUMIF(Attendance!$J:$J,{"Y","A"},Attendance!$D:$D))

I've added a table in the PickLists sheet, and put the corresponding column in there, but can't figure out how to do this? Any help would be amazing and would result in my manager thinking I'm ace (or at least not crap).

Cheers,
John

Replaced "Attendance!$I:$I" with the part below and defined two new names on the attached sheet:
INDIRECT(CONCATENATE("Attendance!",INDEX(Month,MATCH($C$2,Month_List,0),3))

Enjoy!

That's brilliant - thanks! Really appreciate it!!! Works perfectly!

You can probably see what I'm trying to do. Do you think there's a better way of doing this?

Basically what happens is that before the meetings, a report is downloaded, the list of people updated, then the attendance noted which generates the stats.

The thing is, even though the month picker works fine, I've realised that for a previous month, the old data will be wrong because if the list of people is updated or the number of profiles in the roles report changes, this data will be updated, and therefore update previous months data, when I really should time stamp it in some way.

I was thinking of adding a table of historical data, then just having the user copy and paste it? Or is there a better way? Obviously I'm not expecting a solution, just any ideas!

Thanks