Building a Better Raffle

At a staff meeting today, we discussed the idea of incentivizing students to register or update their registration with my organization. In the first month of the school year, we could potentially have about 200 new students register and about 600 previously registered students update their info.

Two incentive options were proposed:

  1. Randomly select 5 students who register/update and give each of them a $20 iTunes gift card.
  2. Randomly select 2 students who register/update and give each of them a $50 iTunes gift card.
So which is more effective at getting students to complete the registration? Would either of them push you more than the other to register? That is, do you want a better chance at winning something small, or a lesser chance of winning something big?