## 4 Discussion  
The present study shows that the error in AVR measurements of the thoracic vertebrae in radiographic images is greater than the error in the measurement of the lumbar vertebrae, and that the reliability of the thoracic and lumbar vertebrae measurements is practically the same (SD = 1.88\({}^{\circ}\) and 1.83\({}^{\circ}\)). However, the mean error in the measurements of the thoracic vertebrae is significantly higher (1.38\({}^{\circ}\) and 0.38). Nevertheless, we have obtained an almost perfect agreement, according to [PERSON] and [PERSON] [39], between the distributions of the two types of vertebrae and their respective gold standard (ICC (2.1) = 0.985 with 95% confidence interval = 0.97-0.993 in the lumbar vertebrae and ICC (2.1) = 0.974 with 95% confidence interval = 0.897-0.99 in the thoracic segment). Knowledge of a measuring instruments' quality is essential, as the diagnosis and treatment decision may depend on its performance. There are significant discrepancies in the validity and reliability of AVR measurements in radiographic tests, according to the type of vertebrae imaged, in the literature. These discrepancies could be justified by the use of different measurement instruments (Raimondi, Perdriolle, Nash & Moe, etc., each with a different validity and reliability), by the type of image support (physical radiography, digital X-ray with different characteristics, and others), as well as by the number of observers and measurements, which in some studies lead to a relatively low statistical power. For example, [PERSON] et al. [6], who used the Perdriolle method and the X-rays of two thoracic and one lumbar cadaveric vertebrae, found no significant differences between the vertebral levels. [PERSON] et al. [26], using the Perdriolle method on the X-rays of five lumbar and five thoracic cadaveric vertebrae, obtained a higher reliability in the measurements of the lumbar vertebrae. [PERSON] et al. [16], using the X-rays of one lumbar and one thoracic cadaveric verteba, obtained, with the Raimondi method, a better agreement between the measurements of the thoracic verteba and the real values; with the Nash & Moe method, they obtained worse measurements in the thoracic vertebrae. [PERSON] et al. [3] studied the AVR in the X-rays of 25 patients with AIS, using the Raimondi method, and they found an error in the thoracic vertebrae of 9.18\({}^{\circ}\)\(\pm\) 3.33\({}^{\circ}\) and 10.18\({}^{\circ}\)\(\pm\) 5.9\({}^{\circ}\) for the lumbar vertebrae. In our study, we have made a more significant number of measurements than in the studies of [PERSON] et al. [6] or [PERSON] et al. [26]. In addition, to our knowledge, our study is the analysis with the largest number of evaluators. In our study, we have calculated, for both thoracic and lumbar vertebrae, the absolute validity and reliability of their AVR measurements, which requires a minimum of 30 clinical  
Figure 4: 95% confidence intervals for the means of the distributions of the measurements of both types of vertebrae. cases, measured by at least six blind observers and a minimum of 3 tests per observer, spaced at least two weeks apart [35; 36]. The medical images which were used have been considered standard in the quantification of AVR in AIS patients, i.e., plain radiographs in DICOM format of the entire spine [9; 23; 24; 29; 30; 31; 32]. The possibility of increasing a vertebra's size with the mouse's scroll wheel allows the correct determination of the reference points. Frequently, determining the width of the vertebra is difficult, due to the overlap of structures, particularly in the dorsal vertebrae, and focusing on the width of the adjacent vertebrae can make that easier. The main reason for an incorrect level determination and worse reliability by using conventional measurement methods is that the vertebra to be measured (the one with the highest torsion) is often determined with the naked eye and then measured.