> For the complete documentation index, see [llms.txt](https://help.bioinsight.illumina.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://help.bioinsight.illumina.com/emedgene/emedgene-analyze-manual/reviewing_a_case/lab_tab/sample-quality-section/array-sample-quality-metrics/log-r-deviation.md).

# Log R deviation

The Log R Deviation (or Log R Ratio standard deviation) quantifies the variability of the the signal intensity for each SNP marker on an array, ie, noise level.

Log R deviation is one of the key metrics used to determine array sample [quality](/emedgene/emedgene-analyze-manual/reviewing_a_case/lab_tab/sample-quality-section/array-sample-quality-metrics/array-sample-quality.md), alongside [call rate](/emedgene/emedgene-analyze-manual/reviewing_a_case/lab_tab/sample-quality-section/array-sample-quality-metrics/call-rate.md).

Lower values indicate more consistent signal intensities. A high Log R Deviation can indicate a poor-quality sample or potential issues with CNV calling.

Displayed to three decimal places.


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