I cant follow this very well.
Try SFCHECK as well which will do the same tests and give a differently
formatted output..
or TRUNCATE which gives you plots of these stats v resolution..
<I^2>/<I>^2 : 2.351 This is higher than the expected value of 2 for untwinned data.
(1.5 for perfectly twinned data)
However it can be distorted by non-crystallographic translation, but you dont
seem to have that..
Or by experimental errors and you need to inspect it in resolution ranges to
detect that - assuming your low res data is more accurate than the high res.
Eleanor
Yingjie Peng wrote:
Dear guys,
I have collected a dataset with the sg as P31. I ran pehnix.xtriage to
analyse the data with
following result:
Twinning and intensity statistics summary (acentric data):
Statistics independent of twin laws
- <I^2>/<I>^2 : 2.351
- <F>^2/<F^2> : 0.788
- <|E^2-1|> : 0.766
- <|L|>, <L^2>: 0.446, 0.270
Multivariate Z score L-test: 3.358
The multivariate Z score is a quality measure of the given
spread in intensities. Good to reasonable data are expected
to have a Z score lower than 3.5.
Large values can indicate twinning, but small values do not
necessarily exclude it.
Statistics depending on twin laws
------------------------------------------------------------------
| Operator | type | R obs. | Britton alpha | H alpha | ML alpha |
------------------------------------------------------------------
| -h,-k,l | M | 0.460 | 0.043 | 0.039 | 0.022 |
| h,-h-k,-l | M | 0.054 | 0.423 | 0.459 | 0.478 |
| -k,-h,-l | M | 0.476 | 0.042 | 0.043 | 0.022 |
------------------------------------------------------------------
Patterson analyses
- Largest peak height : 4.693
(corresponding p value : 0.95672)
The largest off-origin peak in the Patterson function is 4.69% of the
height of the origin peak. No significant pseudotranslation is detected.
The results of the L-test indicate that the intensity statistics
behave as expected. No twinning is suspected.
Even though no twinning is suspected, it might be worthwhile carrying out
a refinement using a dedicated twin target anyway, as twinned structures
with
low twin fractions are difficult to distinguish from non-twinned structures.
The correlation between the intensities related by the twin law h,-h-k,-l
with an
estimated twin fraction of 0.42 %
is most likely due to an NCS axis parallel to the twin axis. This can be
verified by
supplying calculated data as well.
Is it perfect twinning or partial twinning? I am supposed to do MR with this
dataset.
What should I do next with this dataset? Thanks very much.
Best regards,
Yingjie
Yingjie PENG, Ph.D. student
Structural Biology Group
Shanghai Institute of Biochemistry and Cell Biology (SIBCB)
Shanghai Institute of Biological Sciences (SIBS)
Chinese Academy of Sciences (CAS)
320 Yue Yang Road, Shanghai 200031
P. R. China
86-21-54921117
Email: [EMAIL PROTECTED]
