In our paper reporting the permuted-time test for periodicity , the table in Figure 4 and the text of the Discussion should be modified as follows: The % of genes detected by Tu et al.  should be reported as 57.2% rather than 38.1% as currently reported; thus the difference between the methods should be reduced (to 84.7% vs. 57.2%). The discrepancy results from the fact that the absolute number of 3552 transcripts was identified from a smaller subset of pre-selected expression profiles corresponding to known yeast genes, while the Pt-test was applied to the entire set of probesets. We would like to thank two of the co-authors of the Tu et al.  publication, Drs. Rowicka and Kudlicki (UT-Southwestern), for bringing this to our attention.