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<p> [quote] hawkette, I realize that you did it just to come up with some rough numbers, but be careful about splitting the difference between the first and third quartiles (25th percentile and 75th percentile) to derive some sort of median (or "average", as you called it). The split difference isn't really statistically meaningful since, among other things, it doesn't account for the actual distribution of students within the middle 50%, or for the total "spread" of that group. Also, in most--if not all--cases, it won't give you either the true median or the true mean SAT scores for that school.
And no, barrons, it may not be "close enough for most purposes." The distribution of students within that middle-50% range can vary widely from school to school, greatly undercutting the usefulness of the split-the-difference approach. For example, 2 schools could both have a middle-50% range of 1300-1400, but at school "A" most of the students in that range are clustered nearer to 1300, with most of its students in the upper quartile (above the 75th percentile) clustered near 1400. Whereas at school "B" most of the students in the middle-50% are clustered closer to 1400, with the upper quartile distributed more evenly from 1400 to 1600. If we just split the difference of the middle-50% range, the number for both schools would be 1350. However, that would be very misleading, since in fact the median scores of the 2 schools would be very different, as would their mean scores.</p>