Problems can arise when the median or percentile falls in the first or last element with a factor. For example, if you have a rating scale with factors of 1 for Excellent through to 6 for Very Poor, and all respondents rated the product as Excellent, Quantum might report a median value of 0.5, rather than a value of 1.0, which you might expect, as that is the rating everyone gave. The reason for this is that when Quantum looks at the first element in the rating scale, it finds that there is no previous element so it uses a factor of zero for the nonexistent element. The range for Excellent is therefore 0 to 1 and its median is 0.5.

If you have a table of this type, and you want to see a percentile that matches the factor of the element in which all respondents are held, insert a dummy nonprinting n15 element above the first real element, and give it the same factor as the real element. In the example, if you insert a dummy element with a factor of 1 before the Excellent element, the median for all respondents in Excellent would be 1.0 (between 1 and 1).

Here is the axis:

This use of a dummy element does not affect means, nor does it affect the percentile calculation if respondents are more evenly spread across the elements.