Dear users,
I recently ran a model-free analysis on a ~5kDa protein with relaxation data measured at three fields (600, 800 & 900 MHz). For the analysis, I used the fully automated analysis (dauvergne_protocol.py).
At the end of the diffusion tensor optimisation step, a prolate spheroid tensor seemed to be the best description for diffusion, as assessed by AIC. See below the AIC scores for the individual models:
Data pipe k n Chi2 Criterion
sphere 102 204 2479.48833 2683.48833
prolate 89 204 2391.34556 2569.34556
oblate 88 204 2405.33989 2581.33989
ellipsoid 90 204 2405.90291 2585.90291
My question now concerns the 'large' deviation of ~15 units in chi-squared values between the ellipsoid and prolate models. Shouldn't the value of the ellipsoid be smaller than the axially symmetric models, considering that two additional parameters are used in the ellipsoid?
Why is the chi-squared value slightly larger for the ellipsoid than the prolate?
I looked at the individual models and the log files. The optimisation finished after convergence and the analysis didn't report any errors or the like.
Many thanks,
Romel
AIC values