Think of the median as its position in the ordered list, not as the number in that position. Then to compute the quartiles, only use the values in positions above and below the position of the median. So for example if there are three numbers that all equal the median, only the middle one has the median's position.
--- (B=) On Jan 10, 2012, at 11:58 AM, Roger Hui <[email protected]> wrote: > Thanks to you and all other respondents for their helpful replies. > > Do Moore & McCabe offer any guidance on how to compute the medians? > Wikipedia says "there is no universal agreement on choosing the quartile > values". As well, in computing the IQR I have seen methods that make sense > to me but are quite tricky depending on whether #x is odd or even. > > e.g Suppose x is 1 2 3 4 5, 6 7 8 9 10. The descriptions I have seen say > that the median is 5.5. When you then compute the median of the lower half > (q1), you exclude the 5.5, and report that q1 is 3, and likewise q3 is 8. > In contrast, if y is 1 2 3 4 5, 6, 7 8 9 10 11, the median is 6, but when > you compute q1 you *include* the 6 with the lower half, and report that q1 > is 3.5, likewise you include 6 with the upper half so that q3 is 8.5. > > > > ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
