Response Rate Confusion

[CakeQueenWatford]

My message response rate is currently showing as 75% within 24 hrs, -8% in 24-48hrs and 33% after 48hrs. 
I have learnt I need to reply even when a response is not called for but can anyone explain the minus 8%? I have tried Etsy support but they directed me here. 
Thank you 

[CryzalisMasksUK]

There are only other sellers here who can advice you, but can not actually do anything for you regarding your stats and star seller. Never heard of it going into the minus though