Tuesday, June 19, 2012

NO, NO, NO. The wrong idea.

Found on Flickr here with the caption "normal distribution class photo".

A bell-shaped normal curve is not the normal distribution. The curve only describes the distribution. A normal distribution is a particular arrangement of measurements on a number line.

This photo seems to want to depict a normal distribution of the heights of students. If height is the variable of interest, the horizontal axis should be a number line with all the smallest students on the left and those taller would be placed further to the right. If the heights of the students had a bell-shaped histogram we would expect to see very few short students, very few tall students, and most of the students would have heights that fall between those extremes. This photo puts the tall students in the middle and shorter ones on the extremes. Maybe they have illustrated a bell-curve, but no number line is used, so no distribution (normal or otherwise) could be represented.

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