Thirty healthy subjects (15 males, 15 females) were recruited from a population at King Chulalongkorn Memorial Hospital. The subjects were screened by history taking that consisted of previous back-related symptoms, previous surgery, underlying diseases, and physical examination of the spine to confirm that the subjects did not have any spine problems. The subjects were able to perform the proposed positions and had their SVA evaluated by whole spine lateral radiography in four positions: standard posture by standing with the hands on the clavicles with the elbows touching the trunk (TC), standing with the hands holding on to a railing in front of the patient at arm’s reach (TS), sitting with the hands on the clavicles (IC), and sitting with the hands holding on to a railing in front of the patient at arm’s reach (IS) (Figure 1). Sample size calculation was performed using the formula for the required samples per group  for the comparison of two means. With the alpha error at 0.05, the power at 0.8, a standard deviation of 2, and an expected effect size of 2, the minimum sample size required is 16. All subjects provided informed consent. The study was approved by the Institutional Review Board of the Faculty of Medicine, Chulalongkorn University (No. 669/62).
Measurement of the SVA (Figure 1) and other spinal sagittal parameters, such as thoracic kyphosis (TK), lumbar lordosis (LL), C7-T5 angle, T2-T12 angle, and T10-L2 angle, and pelvic parameters (pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS)) (Figure 2) was performed, and the measurements were compared to evaluate whether there were any differences and correlations between the standard positioning (reference position) and the three new positioning methods.
The measurement for each spine and pelvic parameter was defined as follows:
C7–T5 kyphosis: The angle between the cranial endplate of C7 and the caudal endplate of T5.
T2–T12 kyphosis: The angle between the cranial endplate of T2 and the caudal endplate of T12.
T5–T12 kyphosis (TK): The angle between the cranial endplate of T5 and the caudal endplate of T12.
T10–L2 kyphosis: The angle between the cranial endplate of T10 and the caudal endplate of L2.
T12–S1 lordosis (LL): The angle between the cranial endplate of T12 and the cranial endplate of S1.
PI: The angle between the perpendicular line, from the middle of the sacral endplate, extending caudally, and the line extending from the middle of the sacral endplate to the center of the bicoxofemoral axis.
PT: The angle between the vertical axis and the line extending from the middle of the sacral endplate to the center of the bicoxofemoral axis.
SS: The angle between the horizontal axis and the cranial sacral endplate.
The measurement was performed twice for each parameter, with blinding, by a certified orthopedist and a radiologist. The inter-rater correlation of each measurement between the two observers were calculated for every parameter.
The mean, SD and inter-rater measurement correlation was calculated (Table 1). The average values of the two readings were used for further calculation. The Bland-Altman  analysis was used to determine the limit of agreement by finding the mean difference of measurements and two standard errors of deviation above and below the mean difference determine the limit of agreement (Figure 3). The Lin’s concordance correlation coefficient  (Rc) was used to determine the correlation between the positions, which evaluates by measuring the variation from the 45° line through the origin (the concordance line) (Figure 4). The correlation ranges from -1 to 1, with perfect agreement at 1. Statistical Package for the Social Sciences (SPSS Version 22.0) for International Business Machines (IBM) Windows (Armonk, NY) was used for statistical analysis.