What I am writing here are all my speculations. I haven't contacted any schools regarding the reason to my rejections post my acceptance.
When I say mediocre, I meant terrible interviewing skills. I showed sign of nervousness to some of the interviewers. Also, two of my interviewers for different schools were researchers: I have zero research experience. Pretty much they were not really interested in me without research experience; one of them didn't let me talk at all; I just sat there and had to listen to him talk about how great their school was for 10 minutes.
A good number of schools required a writing sample. I am definitely not a good writer. It took me a month to get my personal statement peer reviewed and had to edit the final draft 10+times. Writing samples are given 30 minutes. With lack of sleep due to time difference and tiredness, my grammar wasn't going to be any better, nor was the composition of the writing (also english is my third language). This is why I recommend others to develop good writing skills prior to interviews.
Some schools use a point system just as
@MasterDental said. They categorize each part of application (GPA, DAT, Extracurricular, Research, Interviews) into percentages, add all the points, and rank the applicants.
Some tips that I can give in order to do well for your interviews are the following:
1. PRACTICE PRACTICE PRACTICE!! I cannot emphasize this enough. Have a friend, significant other, a parent, a coworker, or anyone you can find practice interview questions with you. This will help because you'll have a good idea of what you want to say, how to say it, and prevents you from babbling on. If possible, keep your answers to the point; try not to deviate from your core response too much.
2. If you're like me and have to travel across the country for interviews, try to get there 2 nights before the interview day. It may not seem like much, but you'll be much more adjusted and well rested. For a few interviews, I flew the red eye, and it was not a good idea. Exhaustion can cloud what you want to say.
3. Writing may not come as easy as to some, I'd say grab a novel or two, or even three if you have time, and just read. You may even want to just time yourself for 20-30 minutes and see what you can come up with. Use interview questions as topics.
4. If you're not confident, feeling cheerful, or hate where you are, just fake it. I realized that many of the interviewers (students and staff) observe potential candidates to see how they interact with others. It makes sense right? You wouldn't want to hire someone you won't be able to hang out with.
5. Educate yourself! Make sure you are knowledgable about the school. It can include the specific volunteer programs the school offers to a research program you're interested in. By being aware of what's going on the school, it shows that you genuinely want to attend the school (even if you may not).
6. Lastly, be yourself (unless you're a crazy sociopath... then be someone else). Let your true self shine through!
