tigerlilies

I think there are two reasons. The first is that departments are generally pretty good at selling themselves, so whatever attractive aspects led to one applying to a school are magnified during the visits. The second is that putting an actual face to a name makes things more difficult. Meeting professors and graduate students at the programs makes the possibility of attending the schools feel real. Instead of abstract thoughts about taking classes and performing research, it becomes more realistic to imagine oneself there. Instead of just a name that you've emailed with or a campus seen through photo's, the visits humanize the process, at least for me.

Haiku Poem:
Current Yale Grad here.
Yesterday we got invites
To host new admits.
 
At April visits
For the prospective students
So, decisions soon?
 
I think you can take it that decisions are made and coming out soon. Yale does personal notifications from usually POI. Usually email. Some by phone.
Best of luck see some of you soon.

A great way to find these is to look at  methods ABDs' websites; many of these people have taught the "math camp/refresher/etc" and TA-ed for the stats sequence, and often have links to the course materials. For example, here's Harvard's most recent math "prefresher."
David Seigel at Duke also has some really great videos on math for social scientists.

Does anyone know when the visit dates are for Columbia?

DO NOT get drunk and do / say stupid things.
It happens more often than you'd think... 

It has been painful. I got four letters out the gate, first week of February. That was followed by nothing for weeks. i just want some closure so I can get to work on planning the move and what not... and yeah one or two more acceptances would be amazing!

As usual, n=1. So take this with a grain of salt. I committed to School A, only to get off the waitlist at School B on maybe April 16. A couple of weeks later I asked to be let off the hook from School A and committed to School B. Everyone at School A (and at School B, for that matter) was extremely gracious, kind, and understanding. The program administrator at School B liaised with their counterpart at School A so that I wouldn't have to worry about the bureaucracy and could focus instead on making my decision and talking to my POIs at both schools. When I decided to go to School B, I contacted the people I had met with at School A. I didn't go into too much detail, but I did say where I was going, I thanked them profusely, I said I was genuinely sad that I wasn't joining their program, and I noted that personal factors played an important role. I said I hoped we could stay in touch. All of that was sincere.  Every single person wrote back. Like I said, every single person was gracious, kind, and understanding.
So that's my story.* Maybe I got really lucky with the folks I met at School A. Maybe I was also lucky in the sense that, given my profile, the switch made a lot of sense. Maybe. But I still think the things I did right are transferable: Act in good faith. Be honest. Be forthcoming. Get help from administrators. And know that, as I said above, faculty and administrators everywhere know that this is just how the game is played. Try to worry less about pissing someone off and more about making sure that you make the right decision. It's one of the most important you'll ever make.
By the way: if there are other people, not at School A or B, who have been supporting you / following you in this crazy adventure, make sure to keep them in the loop too if you decide to make a last-minute switch. They'll appreciate it. 
*I'm not super comfortable publicly sharing more than what I've already said, but feel free to message me if you want to chat more. 
 

This might help 
Good luck!

If waitlist decisions come out in April and I need to respond to some of my offers before that... what do I do? 

It's rather trashy, in my opinion.

And another day begins...