PanCancerAtlas RNA-SeqV2 (RSEM) file contains negative values

Question

[psychemistz]

I just downloaded "EBPlusPlusAdjustPANCAN_IlluminaHiSeq_RNASeqV2.geneExp.tsv" file from pancanceratlas supplemental data section of the NIH website. https://gdc.cancer.gov/about-data/publications/pancanatlas

During processing, I realized that this file contains negative RSEM values ​​that can be summarized as follows:

Min     1st Qu.    Median   Mean   3rd Qu.   Max.

-0.9912   -0.8951   -0.8633   -0.8613   -0.8168   -0.6687

According to my understanding the value calculated via RSEM means the expected number of mapped reads, so I guess the value should be 0 or positive. Can anybody explain why the expression matrix contains negative values?

Thank you in advance.

[igor]

This previous discussion might be helpful in understanding the contents of that file: What batch correction was applied to pan-Cancer mRNA expression data?

[chengdu_1982]

whether the exp matrix log transformed?

[ATpoint]

Please use ADD REPLY, the answer box is for answers only. That keeps it logically organized.