Resolution limits in xia2

By default the resolution limits produce what I hope is "something sensible" - however there are cases where for perfectly good reasons people may disagree with these. It's therefore about time these were better explained.

The default resolution limits are:

• I/sigma > 1 at the edge
• Merged(I/sigma) > 2 at the edge

These are determined with my own merging code not scala or XSCALE, so there could be some small differences at the end. These are controlled by the command line options -isigma and -misigma respectively, and whichever one is lower  will be used. Some examples are helpful here, so I will use a data set recorded last week on I24 in 9 seconds (how cool is that)

Default run:

High resolution limit                           1.62    7.23    1.62
Low resolution limit                            31.73   31.73   1.66
Completeness                                    99.8    98.6    99.7
Multiplicity                                    5.7     5.3     5.3
I/sigma                                         14.9    35.9    2.4
Rmerge                                          0.066   0.026   0.695
Rmeas(I)                                        0.073   0.028   0.771
Rmeas(I+/-)                                     0.073   0.028   0.771
Rpim(I)                                         0.03    0.012   0.328
Rpim(I+/-)                                      0.03    0.012   0.328
Wilson B factor                                 19.666
Partial bias                                    0.0     0.0     0.0
Anomalous completeness                          98.1    100.0   95.9
Anomalous multiplicity                          3.0     3.6     2.7
Anomalous correlation                           -0.028  -0.093  -0.015
Anomalous slope                                 0.973   0.0     0.0
Total observations                              193625.0        2465.0  13041.0
Total unique                                    33686.0 465.0   2438.0

Being very cautious - merged and unmerged I/sigma > 2:

-isigma 2 -misigma 2 (unmerged I/sigma will dominate)

High resolution limit                           1.78    7.94    1.78
Low resolution limit                            31.73   31.73   1.82
Completeness                                    99.8    98.1    99.8
Multiplicity                                    5.9     5.2     5.5
I/sigma                                         18.7    35.6    4.8
Rmerge                                          0.058   0.025   0.338
Rmeas(I)                                        0.063   0.028   0.374
Rmeas(I+/-)                                     0.063   0.028   0.374
Rpim(I)                                         0.026   0.011   0.157
Rpim(I+/-)                                      0.026   0.011   0.157
Wilson B factor                                 18.981
Partial bias                                    0.0     0.0     0.0
Anomalous completeness                          98.8    100.0   96.6
Anomalous multiplicity                          3.1     3.6     2.8
Anomalous correlation                           0.004   0.261   -0.001
Anomalous slope                                 0.98    0.0     0.0
Total observations                              150435.0        1872.0  10262.0
Total unique                                    25633.0 362.0   1872.0

Being very generous - unmerged I/sigma > 0.2, merged > 1:

-isigma 0.2 -misigma 1 (merged I/sigma will dominate)

High resolution limit                           1.51    6.75    1.51
Low resolution limit                            31.73   31.73   1.55
Completeness                                    99.8    98.9    99.3
Multiplicity                                    5.5     5.2     4.1
I/sigma                                         12.5    35.4    1.2
Rmerge                                          0.074   0.026   1.095
Rmeas(I)                                        0.081   0.029   1.253
Rmeas(I+/-)                                     0.081   0.029   1.253
Rpim(I)                                         0.034   0.012   0.594
Rpim(I+/-)                                      0.034   0.012   0.594
Wilson B factor                                 19.471
Partial bias                                    0.0     0.0     0.0
Anomalous completeness                          96.9    100.0   88.8
Anomalous multiplicity                          2.9     3.5     2.2
Anomalous correlation                           -0.042  0.072   -0.038
Anomalous slope                                 0.97    0.0     0.0
Total observations                              228772.0        2991.0  12145.0
Total unique                                    41226.0 570.0   2964.0

There are also limits you can apply in terms of Rmerge etc, however these are essentially the same as limiting the unmerged I/sigma as Rmerge ~ 0.8 / (unmerged I/sigma)