Am J Orthod Dentofacial Orthop 2017;151:222-3
Sometimes we are interested in comparing pairs of observations within the same subjects. Then we should bear in mind that those observations are not independent and should be treated accordingly. Let us consider the scenario where we are planning a study to assess the effectiveness of a new cone-beam computed tomography (CBCT) device with a lower radiation dose (device A) compared with the standard panoramic radiography (device B) in identifying early lateral incisor root resorption in subjects with impacted canines. Table I shows the results of the 2 devices for the same 30 subjects in terms of identifying root resorption (1) or no resorption (). We can see that in some subjects, a, both devices identify root resorption (1 1); b, device A identifies root resorption (1) but device B does not (); c, device B identifies root resorption (1) but device A does not (); and d, neither device identifies root resorption ( ).