A few hosts have commented on their response rate not accurately reflecting their actual responses.
Because I am having the same experience, I contacted Airbnb two days ago about my response rating not accurately reflecting my responses according to THEIR definition.
Their reply: The number we see is based on the past 12 months (or maybe from 1 Jan ... ?) and not on the past 30 days (90 if fewer than 10 messages). This number is not visible to guests (anyone have feedback on whether this is accurate or not?). The response ratings for the past 30 days will be visible on the listing details itself; this feature is being rolled out so some of us may see it, while others will be seeing it at a later date. I don't see my response rating yet, but I'll be watching for it.
To see where the response rate will be located, go to your listing and scroll all the way down to your profile located immediately above the map. Airbnb rep says they'll be placing the rating in the blank space to the right of About the Host/Contact Host.
Hope this helps (and I [emphasized] hope the CSR was giving me accurate information--to his credit, the CSR put me on hold several times to get indepth information from staff who knew more about this issue).
Hosting since Thanksgiving Day 2012 and over 1,000 stays. May you ever be the benevolent ruler of your own domain--YOUR life. Allow no other to rule over it.