> -----Original Message-----
> From: [log in to unmask] [mailto:[log in to unmask]]
On
> Behalf Of Eleanor Dodson
> Sent: 23 April 2009 15:59
> To: Kumar
> Cc: [log in to unmask]
> Subject: Re: [ccp4bb] Twinning or not?
>
> Look at the moment plots after scalepack2mtz; if these are normal it
> seems very unlikely you have twinning..
> Eleanor
I know this subject has been beaten to death in previous BB discussions,
but is it always as clear-cut as this? If for example you had a NCS
2-fold co-incident with the twinning axis wouldn't that bias the moment
stats? The derivation of the moment stats in the twinned case assumes
that the pairs of twin-related intensities (assuming we're talking about
the hemihedral case) are statistically independent, but that assumption
is clearly invalidated if there's NCS parallel to the twinning axis, and
in that situation the moment stats would tend towards the untwinned case
(depending of course on the exactness of the NCS and the resolution).
It's of no consolation to someone to tell them that their situation is
very unlikely if it actually happens to them!
It seems reasonable to say that if the moment stats conform to the
twinned case, then twinning is almost certainly present (barring data
processing blunders); however if the moment stats conform to the
untwinned case then you can't say for sure that it's not twinned,
there's still a chance (maybe small) that it's twinned even if the data
has been correctly processed.
I've read on several occasions that twinning and NCS are quite likely to
occur together, but I wonder if anyone has done a proper analysis and in
particular looked at cases where the twinning & NCS axes coincide to see
the effect on the moment stats?
Cheers
-- Ian
Disclaimer
This communication is confidential and may contain privileged information intended solely for the named addressee(s). It may not be used or disclosed except for the purpose for which it has been sent. If you are not the intended recipient you must not review, use, disclose, copy, distribute or take any action in reliance upon it. If you have received this communication in error, please notify Astex Therapeutics Ltd by emailing [log in to unmask] and destroy all copies of the message and any attached documents.
Astex Therapeutics Ltd monitors, controls and protects all its messaging traffic in compliance with its corporate email policy. The Company accepts no liability or responsibility for any onward transmission or use of emails and attachments having left the Astex Therapeutics domain. Unless expressly stated, opinions in this message are those of the individual sender and not of Astex Therapeutics Ltd. The recipient should check this email and any attachments for the presence of computer viruses. Astex Therapeutics Ltd accepts no liability for damage caused by any virus transmitted by this email. E-mail is susceptible to data corruption, interception, unauthorized amendment, and tampering, Astex Therapeutics Ltd only send and receive e-mails on the basis that the Company is not liable for any such alteration or any consequences thereof.
Astex Therapeutics Ltd., Registered in England at 436 Cambridge Science Park, Cambridge CB4 0QA under number 3751674
|