Actually there is a science to it. If there are 10 people in the pool with scores of: 410, 430, 435, 444, 438, 464, 450, 455, 445, 440. CIC takes the average of those scores and would invite anyone at or above the average score which in this case would be 441. The number of people invited for each draw is a percentage of the pool size. The recent trends point to 4.11% or less of the total pool size. In this example the top 5 people at or above 441 would have been given an invite barring other factors like the tie breaker rule etc.