Eye Fitting Straight Lines

Because little is known about properties of lines fitted by eye, we designed and carried out an empirical investigation.Inexperienced graduate and postdoctoral students instructed to locate a line for estimating y from x for four sets of points tended to choose slopes near that of the first principal component (major axis) of the data, and their lines passed close to the centroids.Students had a slight tendency to choose consistently either steeper or shallower slopes for all sets of data.