In NCBI GEO website, We can find the expression dataset sample. I need to know how this expression value is calculated based on the raw data. In other words, What methods are used to transform raw values to a single expression value? I appreciate your help to figure out the sample dataset which I have been referring here.
That depends from dataset to dataset, however, if you read the content of the page you are linking to, you will find the description:
Data processing The scanned images were analyzed with Feature Extraction Software 220.127.116.11 (Agilent) using default parameters to obtain background subtracted and spatially detrended Processed Signal intensities. The intensity signals was imported to CLC Main workbench 6.0 and normalized by the quartile normalization method and log2 transformed.