How do you answer the Questions "How Many Members did we have last year?"

For organizations that have one or more membership programs, I was wondering HOW you answer this type of question regarding Members:

• How many members did we have: 
  • Yesterday?
  • Last Quarter?
  • Last Year?
  • 26 months ago?

I'm NOT interested in the specific numeric answer for your organization.

* I'm looking for a description of where you go to answer this type of question when asked.

• Do you use: 
  • Use A List.
    • Base on what criteria?
  • T-Stats
    • What kind of setup?
  • Do you have a spreadsheet where you are keeping this kind of data.
    • What data do you keep and how often
  • Do you use a customization unique to your organization
    • What is the nature of the customization
• Or are you not really able to answer this question.  
  • And when pushed do you give another answer like the number of households donating to a membership campaign for a specific fiscal year?  Or some other operationalization of the question.

* Second, based on your answer above.  How "accurate" and useful is your answers regarding the general question?

• Where do you think your method of answering this question could more specifically answer this question?
• Do you know of cases where your answer is getting it wrong?
• Can you scale your answer up and down regarding time periods?
  • How many members did we have the last two years
• Do you have any way to use these answers to predict future growth?
• How quickly would your method to answering this question show that you were gaining or losing members? 
  • (What is the shortest period that could show a change from one period to the next?)

Lots of questions here.  Answer what interests you.  You can reply here or send me a private message at tbrown@bam.org

Thanks for any insights you can provide on the membership count question.  This is a question that comes up around here fairly regularly and I'm asking the questions as part of preparing for a TLCC 2014 session on Membership BI.