Oh, I thought the sigmas were derived from the differences in intensities of the multiple measurements of a given reflection--I guess both the individual-measurement counting stats and differences in measurements must be combined in the end. But, what does the software do if somehow a sigma=0 creeps in, or more generally, what is the best statistical approach for this?<div>
<br></div><div>JPK<br><br><div class="gmail_quote">On Thu, Aug 23, 2012 at 12:44 PM, Jim Pflugrath <span dir="ltr">&lt;<a href="mailto:[log in to unmask]" target="_blank"><a href="/cgi-bin/wa-jisc.exe?LOGON=A3%3Dind1208%26L%3DCCP4BB%26E%3Dquoted-printable%26P%3D5739129%26B%3D--047d7b3441004d31bf04c7f28533%26T%3Dtext%252Fhtml%3B%2520charset%3DISO-8859-1%26pending%3D" target="_parent" >[log in to unmask]</a></a>&gt;</span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">




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<div style="direction:ltr;font-size:10pt;font-family:Tahoma">Singly-measured reflections should have a sigma from Poisson counting statistics, so that should not be a problem.  A problem might occur if the X-ray background is exactly zero
 and the observed (sic) intensity is exactly zero.
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<div style="direction:ltr"><font face="Tahoma" color="#000000"><b>From:</b> CCP4 bulletin board [<a href="mailto:[log in to unmask]" target="_blank"><a href="/cgi-bin/wa-jisc.exe?LOGON=A3%3Dind1208%26L%3DCCP4BB%26E%3Dquoted-printable%26P%3D5739129%26B%3D--047d7b3441004d31bf04c7f28533%26T%3Dtext%252Fhtml%3B%2520charset%3DISO-8859-1%26pending%3D" target="_parent" >[log in to unmask]</a></a>] on behalf of Jacob Keller [<a href="mailto:[log in to unmask]" target="_blank"><a href="/cgi-bin/wa-jisc.exe?LOGON=A3%3Dind1208%26L%3DCCP4BB%26E%3Dquoted-printable%26P%3D5739129%26B%3D--047d7b3441004d31bf04c7f28533%26T%3Dtext%252Fhtml%3B%2520charset%3DISO-8859-1%26pending%3D" target="_parent" >[log in to unmask]</a></a>]<br>

<b>Sent:</b> Thursday, August 23, 2012 12:36 PM<br>
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<b>Subject:</b> [ccp4bb] Calculating I/sig when sig = 0<br>
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<div>Dear Crystallographers,
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<div>what approach is taken to calculate I/sig when sig = 0? (This could happen for singly-measured reflections or perhaps some other scenario, such as rejection of other measurements leaving only one measurement.) I could imagine alternatives, but what is
 actually done?</div>
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<div>JPK</div>
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Jacob Pearson Keller<br>
Northwestern University<br>
Medical Scientist Training Program<br>
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</blockquote></div><br><br clear="all"><div><br></div>-- <br>*******************************************<br>Jacob Pearson Keller<br>Northwestern University<br>Medical Scientist Training Program<br>email: <a href="mailto:[log in to unmask]" target="_blank"><a href="/cgi-bin/wa-jisc.exe?LOGON=A3%3Dind1208%26L%3DCCP4BB%26E%3Dquoted-printable%26P%3D5739129%26B%3D--047d7b3441004d31bf04c7f28533%26T%3Dtext%252Fhtml%3B%2520charset%3DISO-8859-1%26pending%3D" target="_parent" >[log in to unmask]</a></a><br>
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