Dora et al1 investigated spinal canal dimensions in patients with herniated spin

Question

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.) Some of the patients were due to undergo discectomy (removal of part of a ruptured disc) to alleviate their symptoms of lower back pain or leg pain. The other patients also had disc herniation, but without experiencing symptoms. These asymptomatic patients were identified from hospital records of cases unrelated to back pain, from which patients were chosen that matched the symptomatic patients by 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.

Explanation / Answer

This experiment sounds like a case-control study where we are trying to study the effect of experiencing symptom on the spinal canal cross-sectional area between vertebrae L5/S1 by controlling the inwanted variables like Age, Sex etc.

We want the participants in this study to share same characteristics except the one under consideration.

So, the samples are obviously no more independent. These are called matched pairs and hence the data is paired.

So, the study must be analysed as paired sample data.

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