"Ben, I submitted my application early December and have not heard anything yet. From what I understand from your posts, not getting an interview at this point is not reflective of my strength as an applicant, is that correct? Also, when an AdCom member reads an application, what are the possible ratings that are given? Is it: Yes, No, Maybe, Invite for interview, etc? If an application passes through two readers without being called for an interview, does it mean that the readers did not think that the application was strong enough? Can a person be called for an interview after the application goes to the committee?"
We are actually still reading applications from December. Not knowing who you are, I don't know if you're with a first reader, second reader or waiting to go to committee. But, given that you submitted in early December, you're probably somewhere in the pipeline.
A person can get invited to interview after the first read, the second read, or the committee can decide to interview someone who was not put through for an interview by either of the readers. There's no hard-and-fast rule regarding strength of application and timing of invite.
Hope this helps!