Skewness — I think the idea a distribution has a shape is something that some students just don’t grasp, and I’ve never got a good grip on what it is that blocks them from understanding concepts like skew (they get outliers at least in the broad, conversational sense, but skew remains a mystery). The weirdest thing is you can actually have students make a histogram complete with counting and choosing bin size and graphing and the whole bit, and they still do not get at a deep level what a distribution is.

If anyone has some killer activities here, let me know. My sense is that a long exposure to bar charts tends to push them to view histograms as ordered but categorical data…

Chart above from Biostatistics: A foundation for analysis in the health sciences.