got this from
http://www.***********/healthcare/Exams/nclex.shtml
"
After you have answered the minimum number of questions, the computer compares your competence level to the passing standard and makes one of three decisions:
One, if you are clearly above the passing standard, you pass and the examination ends.
Two, if you are clearly below the passing standard, then you fail and the examination ends.
Three, if your competence level is close enough to the passing standard that it's still not clear whether you should pass or not, then the computer continues to ask you questions.
"Clearly" passing or failing is defined as when the "gray zone" around your competence level falls entirely above or below the passing standard. The gray zone is the region within which your competence level might vary if you answer more questions. The gray zone shrinks a little after each question because your competence level is based on more information.
After each question, your competence level and the gray zone are recomputed, adding your new response to all of your previous answers. When the gray zone is entirely on one side or the other of the passing standard, you've clearly passed or failed and the examination ends.
Of course, some people's competence level is very close to the passing standard. For some of these people, all 3,000 questions in the item pool still might not be enough to make it "clear" whether they should pass or fail. These are the people who take the maximum number of questions. At that point, the computer disregards the gray zone and simply looks at whether the final competence level, based on every question answered, is above or below passing. If you are above it, you pass. If not, you do not pass.
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hope this helps ..... good luck...