# How do I know what side is skewed? [duplicate]

If I look at a quantile plot comparing normal distribution and other data, and some of the points lie below or above the line, how do I know what that represents? What I am asking is - how do I know if the data set has a left or right skew?

• Do you want to edit your post to include an example plot so someone can give you a concrete response? – mdewey Jan 31 '17 at 9:03
• Are you asking about a quantile-quantile plot or some other plot involving quantiles? If so, does this question solve your problem? – Glen_b Jan 31 '17 at 10:46
• I am not anxious to re-open a discussion that has already happened, but I hold that skewness is not a single Platonic property but definable by scalar measures in numerous different ways. That point of view is expounded in the thread I cited. Just two minute examples: a Weibull with moment skewness is not symmetric; there are many binomials with mean = median = mode which are graphically skew. – Nick Cox Feb 1 '17 at 17:20
• @NickCox Skewness has to be defined before one can reasonably expect any plot to reveal skweness. Pick one. Using the moment definition, one can numerically calculate skewness for distributions that have no defined skewness, e.g. Student's t for $v\leq 3$. One cannot then invert the Q-Q graph and talk about relative tail heaviness for tails that are of random heaviness. – Carl Feb 1 '17 at 17:48
• I can only speak for myself with authority. I thought of skewness just using graphs for many years without paying very much attention to ways to define it precisely. Once I had learned of ways to measure skewness, I then had to unlearn the idea, or move towards the further idea that there are many possible measures and one can jump between them according to the problem. – Nick Cox Feb 1 '17 at 18:17