Reply to Hartl and Gao: Lack of between-batch difference in the distributions of measured extracellular RNA levels

We thank Drs. Hartl and Gao for pointing out the difference in read lengths between the cancer and normal samples (1). Indeed, Illumina discontinued their 50-base pair (bp) sequencing kits after we finished sequencing the cancer samples, forcing us to switch to 75-bp sequencing kits on the normal samples. The different sequencing kits did incur small changes of sequence alignment metrics. While acknowledging the possibility that this may bias the assessment of cancer vs. normal discrimination performance of our method, we believe such a possibility is substantially ameliorated by the following considerations. First, a recent study reported that “with the exception of 25 bp reads, there is little difference for the detection of … [↵][1]1To whom correspondence may be addressed. Email: shuchien{at}ucsd.edu, hisu{at}ucsd.edu, or szhong{at}ucsd.edu. [1]: #xref-corresp-1-1