Dear Morphometricians, 

I have a weird problem and I was hoping someone could help me on this. 

I have the same CT bone (n=400) with 14 landmarks (2 Single point and 12 
sliding) larndmarked in IDAV Landmark by three different individuals 
following a figure key table. Each individual landmarked 100+ different 
bones. The figure key table has the shape of the bone, with the landmark 
locations and the order of landmarking. All users were briefed by a single 
person (user1) on how to extract the bone and landmark. All three 
individuals were present throughout the entire procedure but the bone 
segmentation and landmarking process was conducted individually. 

When I combine all the data, I noticed that PC1 and PC2 graph has two 
clusters. The effect is about 55% (as detailed in the eigenvalues below) 
After further checking the classifiers in MorphoJ, the source of the 
clustering is one person (user1) landmarked it is slightly differently 
compared to the other two. I have checked the outliers tab and no glaring 
outliers exists. As the sample size is big, the curve seem to be quite 
normal. 

Eigenvalues          % Variance     Cumulative %
  1.     0.01603351      55.674       55.674
  2.     0.00496222      17.230       72.904
  3.     0.00224594       7.799       80.703
  4.     0.00121085       4.204       84.907
  5.     0.00076858       2.669       87.576
...

How to interpret the results for this kind of data? Things which come to my 
mind are:

1. Maybe the bones for user1 are different compared to the other two users.
Or 
2. User1 thinks the landmark location slightly different compared to others.
Or
3. User2 and 3 could not locate the landmark locations of user1.
Or
4. The landmarks selected are unreliable.

Ideally I would need few other people relandmark the entire set, but it is 
not possible to do it now. Can anyone help shed some light on what is the 
probable cause? Thank you.


Kind regards,

Helmi Hadi, PhD
 School of Health Sciences, Universiti Sains Malaysia,
16150 Kubang Kerian, Kelantan, MALAYSIA


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