## 2 Method  
### Participants and Data Collection  
A survey was conducted in order to collect anthropometric data of children's heads and faces [28; 40]. A total of 302 Dutch children (128 females, 174 males) aged 6 monthsto 7 years were recruited through health centres, primary schools and the university. Of the total population, 17.8% (\(n=54\)) children were considered to be of non-native Dutch origin. This was defined as when the country of origin of either one or both of the child's parents was not the Netherlands. The anthropometric survey was approved by the Human Research Ethics Committee of the Delft University of Technology. Informed consent was obtained from all participants involved in the study. Age categorisation was done according to ISO 15535 [41], which describes the general requirements for establishing anthropometric databases. Age groups were divided as follows: individual age for age group 1 is 0.50 to 1.49 years; for age group 2, it is 1.50 to 2.49; and, for age group 3, it is 2.50 to 3.49, etc.  
In the survey, both traditional anthropometric measurements as well as 3D image derived measurements were collected as described in [PERSON] et al. [28] through a five-step procedure. First, the following traditional anthropometric head and face dimensions were recorded; head circumference, head length, head height, head width, and face width, as well as more general measurements such as stature and weight. Second, four 3D images captured from different directions per participant were collected using the 3 dMD Face system (3 dMD Ltd., London, UK). All children were scanned with a neutral face expression. These images were then combined into a 360 degree 3D image of the head. using Artec Studio 9 software (Artec Group, Luxembourg) and the remaining holes in the image were repaired in Geomagic Studio 2013 software (3D Systems, Rock Hill, SC, USA). After that, a total of nineteen landmarks were marked on each 3D face with 3 dMD Vultus 2.1 software (3 dMD Ltd., London, UK) as shown in Figure 1. The landmarks that were included in the survey could be identified on the 3D image without palpation. The definitions of these landmark locations can be found in [28]. Finally, eight facial dimensions were measured and extracted after the 3D images were aligned according to the Frankfort horizontal plane ([PERSON], 1988) using MATLAB(tm) software (The MathWorks, Inc., Natick, MA, USA). An overview of the full procedure is illustrated in Figure 2. Table 1 shows the summarized information of the data including mean and standard deviations for each dimension per age group, males and females combined.  
Figure 1: The landmarks included in this study; 1. glabella, 2. sellion, 3. pronasale, 4. subnasale, 5. Sublabiale, 6. Pogonion, 7. menton, 8/9. nasal root point, (right/left), 10/11. endocanthion (right/left), 12/13. infraorbitale (right/left), 14/15. tragion (right/left), 16/17. alare (right/left) and 18/19. chelinion (right/left) [28].  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Age Group 1**} & \multicolumn{3}{c}{**Age Group 2**} & \multicolumn{3}{c}{**Age Group 3**} & \multicolumn{3}{c}{**Age Group 4**} & \multicolumn{3}{c}{**Age Group 5**} & \multicolumn{3}{c}{**Age Group 6**} & \multicolumn{3}{c}{**Age Group 7**} \\  & \multicolumn{3}{c}{**(_t_ = 33)**} & \multicolumn{3}{c}{**(_t_ = 28)**} & \multicolumn{3}{c}{**(_t_ = 29)**} & \multicolumn{3}{c}{**(_t_ = 32)**} & \multicolumn{3}{c}{**(_t_ = 67)**} & \multicolumn{3}{c}{**(_t_ = 65)**} & \multicolumn{3}{c}{**(_t_ = 49)**} \\ \cline{2-13}  & **Mean