Signal Log Ratio Algorithm (SLR)
The Signal Log Ratio algorithm measures the magnitude and direction of change between transcript levels of the experimental and baseline chips. The use of logs in the analysis between the probe sets eliminates difficulties caused by one very high data point in the set masking information from lower valued data points. Base 2 is used as the log scale, therefore a SLR of 1 represents a two-fold increase in abundance of an mRNA and a value of –1 represents a two-fold reduction in transcript expression.
The following formula can be used to calculate linear fold-change from the Signal Log Ratio value.
When SLR is greater or equal to one then Fold change = 2 SLR
When SLR is lower or equal to minus one then Fold change = (-1) X 2 –(SLR)
Forward to Problems associated with Affymetrix GeneChip analysis of Arabidopsis gene expression