[Chances of admittance if I got an invitation to interview?]

I do not know specifically for CEE, but for ECE an interview is pretty much an admission.  I was admitted to Duke's PhD ECE in fall 2015 and that's what my group members told me.

[Is this an interview or actually just a visit?]

Thanks for the replies, that's kind of what I figured. What do you think my chances are of getting funding for a PhD in ECE with these stats:

GPA: 3.6 (3.55 in major) from large state school

GRE: 163Q 161V 4.5AW

2 years research in field of choice with no publications but we are working on a project that will be published soon (but not before the decision is made)

1.5 years research in somewhat related field with one publication (coauthor) in IEEE transactions

3 summer internships at large defense contractor

3 good LORs from my supervisors at each of these experiences

[Is this an interview or actually just a visit?]

I was invited to visit Duke for a "visitation event." I was promised the chance to meet potential faculty advisors but there was no mention of a formal interview and the program (PhD ece) makes no mention of interviews in the application process on their website. The schedule for the event is mostly social activities and tours. While I know that I should treat it as an interview (as I have not yet been admitted) in wondering if this is a good sign that I will likely be admitted or if this is just the next step in the review process. Has anyone experienced a situation like this? It seems like I received the invitation quite early (about 3 weeks after applying) for it not to be a sign that my application was strong.