Dr. Wicklin,

This series is great, I've picked up a lot of good stuff from it.

This particular measure (Hogg's) makes sense, but it's a bit nonintuitive to me in terms of interpretation (and there's quite a bit of computing to do). I know there are other forms of percentile-based skewness (really, symmetry) but I have a question about a form that seems useful to me (I don't know, maybe it's too simple).

Let's say I define a measure of symmetry like this (X## is the ## percentile):

if X95 - X50 > X50 - X05 then my_sym = (X95 - X50)/(X50 - X05) - 1
if X95 - X50 = X50 - X05 then my_sym = 0
if X95 - X50 < X50 - X05 then my_sym = -(X50 - X05)/(X95 - X50) + 1

This gives me a quick take on symmetry, it's zero if the two spreads I'm using are the same, and it ignores outliers. Am I way off here? I'd like a measure that feels a bit more like standard skewness.

Thanks,
Joe