Let's say that there were 1,000 customers who had primarily transacted at a branch prior to the branch's announced closure. Among this cohort, 40 customers closed their accounts with the bank the month following closure, and another 20 customers closed their accounts with the bank two months following closure. If I want to measure the rate of attrition post-closure for the second month, should the denominator be 1000 or 960 (1000 minus the 40 who left in the prior month)?
- Consider the analogy to stock pricing. If a stock is at 10, and goes to 11, it goes up 10%. If it then goes up to 12, it only goes up 9.1%. Your monthly attrition is relative to what you have at the start of the month