The Sorting Ceremony is a test based on the characteristics of the four houses described in the Hogwarts section:
The test is a attitudinal test, so it won’t be of course accurate at 100%, but if you reply sincerely there’s a good chance that your house will be the real one.
To be 100% part of an house you should do the minus points indicated, the more you get close to the next house, the more you get close the higher probability you have to be part of the next house.
This does not means that your attitude, is the House immediately after: the disposition of the Houses are just based on the score of the test.
For example if you totalise an amount of 8 points, you are a Ravenclaw. Not a 100% Ravenclaw, since you should have done 0 points, you still miss at least 4/5 points to be a Gryffindor, this does not means you have an attitude for Gryffindors.
Talking about the Standard Error instead is another story: the more you get close to the next house the easier it is that you belong to that house more than the one you resulted:
For example if you totalled 18 points, at 19 the Gryffindors stop, and at 20 begin the Hufflepuffs, it’s more probable you belong in Hufflepuff rather then in Gryffindor.
Muggle Worthy Case 