*2.3. Data Analysis*

The "4D average" measurement approach used meant that 12 individual values per participant were exported for every spine parameter. Several clinically inconclusive extreme values and, for one participant, isolated missing data points were identified in a preliminary visual data review. The Statistical Package of the Social Sciences (IBM SPSS Statistics for Windows, Version 23.0. Armonk, NY, USA: IBM Corp.) was used to systematically identify these values for every analyzed parameter, and all the extreme outliers revealed by the stem-and-leaf plot were removed from the raw dataset. The missing values were treated as extreme outliers, and the respective cells were removed from the raw dataset as well. The remaining values for every parameter were aggregated to finally create one mean value for every participant and for every parameter of interest.

Descriptive statistics were used to describe the reference values for all the specific (C7–L4 and the pelvis) and global spine parameters according to the mean of means (MoM) and the standard deviation (SD) in all three dimensions for the entire group, for all the female and all the male participants, and for the female and male participants within the three different age cohorts, respectively. An explorative two-way analysis of variance (two-way ANOVA) was used to check for possible differences between the groups according to sex, age cohort or a combination of both (level of significance *p* < 0.05). Possible deviations from the symmetrical zero positions of the different spine parameters were checked by one-sample Wilcoxon signed rank tests (level of significance *p* < 0.05). Graphical figures were created using Microsoft Excel (Microsoft Corporation, Version 2016. Redmond, WA, USA).

The authors do not include a detailed definition or description of the analyzed global and specific spine parameters. Instead, the reader is referred to the respective previous publications [19,24].

#### **3. Results**

#### *3.1. Participants*

A total of 201 healthy participants (132 females and 69 males) were included in the data analyses and were subdivided into three different age cohorts (67 participants per group). Their detailed characteristics, according to age and BMI, are presented in Table 1.

#### *3.2. Data Analysis*

The spinal posture data were analyzed using descriptive and explorative statistics. Reference values for the specific and global spine parameters are presented in Table 2 for the transversal plane, in Table 3 for the coronal plane and in Table 4 for the sagittal plane. Figure 2 (transversal), Figure 3 (coronal) and Figure 4 (sagittal) are the respective graphical representations of the specific spine parameters for those three investigated planes. The results of the explorative statistical analyses are presented in Table 5.


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*Bioengineering*

 **2022**, *9*, 809


