Dora et al1 investigated spinal canal dimensions in patients with herniated spinal discs. (A spinal
disc is "herniated" when some of its soft inner material pushes out through a crack in its tougher exterior.) The patients were in two groups. The "symptomatic" patients were due to undergo discectomy (surgical removal of part of a ruptured disc) to alleviate their symptoms of lower back pain or leg pain. The "asymptomatic" patients also had herniated spinal discs, but withoutexperiencing symptoms. The asymptomatic patients were selected from hospital records of cases unrelated to back pain, and they were chosen so that, for each symptomatic patient, there was an asymptomatic patient with the same age, sex and occupational risk factors. Those selected were then invited to participate in the study. Among other things, the study explored the possibility that spinal canal cross-sectional area might differ between symptomatic and asymptomatic patients.
For all subjects, an MRI scan was used to measure the spinal canal cross-sectional area between vertebrae L5/S1.
Should data from this study be analysed as independent samples or as paired samples? Justify your answer.
[Note 1: need reasons]
[Note 2: a fully correct answer to this question can be written in two or three lines of text]