Yesterday, block information was released for the 2008-2009 academic year. For the classes of 2010 and 2011, this also marked the first in-practice demonstration of the new housing lottery system.
While the new system is designed to be more fair, so it is powered by a program which removes most chance from the system. The core idea behind the program is to have every Swarthmore’s students three housing lottery numbers average out to the same number.
The Rising Sophomore Lottery
This lottery is very simple—-the members of the rising sophomore class are randomly sorted and then assigned sequential numbers.
The Rising Junior Lottery
This is where things start to get complicated.
Every student’s number are first adjusted based on the housing decisions made for sophomore year. Students who decided to block are penalized by the number of students in their class divided by three–this means members of the class of 2011 who blocked will be penalized roughly 122 points. New students (like transfers) are randomly assigned numbers.
This leaves the the College with an ordered list of adjusted-sophomore housing numbers. At this point, the program moves halfway down the list and assigns the middle student the top number in the Junior class. The list wraps around, so the student with the best number in their sophomore year would get the middle number their junior year.
Imagine six students. We’ve assigned them each a number in the sophomore housing lottery (the first number in parenthesis).
If Tim and Sally blocked, their effective-sophomore numbers would move up 2, so the adjusted list is created and then Junior numbers assigned (in brackets).
Jill (1) 
Tim (1) 
Bob (2) 
Sue (4) 
Sally (4) 
Jeff (5) 
The Rising Senior Lottery
This system won’t be implemented until the 2009-2010 school year.
The ranking is determined based on the sum of the student’s previous numbers, as no students are penalized for blocking. Senior lottery numbers are assigned such that the student with the worst sum is given the best senior number. Returning to our example, the sum is in parenthesis and the senior lottery number is in brackets.
Jill (5)  – Total: 11
Sue (5)  – Total: 10
Tim (6)  – Total: 10
Sally (6)  – Total: 9
Bob (8)  – Total: 10
Jeff (8)  – Total: 9