A Boolean variable specifying the presence or absence call.
Warning
This function is not called by the user directly.
References
W. Johnson E., L. Chen, Rabinovic, and A. Adjusting batch effects in microarray
expression data using Empirical Bayes methods. Biostatistics, 8(1):118-127, January2007. ISSN 1465-4644. doi: http://dx.doi.org/10.1093/biostatistics/kxj037.