Percentage chance on any given day that my doorbell will ring at least once between the hours of 4PM and 6:30PM: 80. 

Percentage chance that the dog will bark insanely upon hearing the doorbell ring: 100. 

Percentage chance that the person ringing the doorbell is actually one of my children amusing themselves: 95. 

Percentage chance that I will manage to retain my sanity over the next five years: 15.