The Nation wanted to maintain balance between Free States and Slave States
Explanation:
According to the Missouri Compromise in 1821, there had to be a balance between Slave States and Free States - so anytime a state was admitted as a Slave State - the next state had to be a Free State.
The reason why surveying a different number of people or different population of people can possibly change the percentages that you calculated is because these surveys are simply "samples" of the general population as a whole, and are not exact in terms of their results given any random sample.
