Studying Discrepancies

Having conducted an evaluation as described above, a common question is “what were the errors?” bxb and rxr can help answer such questions.

bxb can generate an output annotation file (with annotator name “bxb”) in which all matching beat annotations are copied from the test annotation file, and each mismatch is indicated by a NOTE annotation, with the aux field indicating the element of the confusion matrix in which the mismatch is tallied (e.g., “Vn” represents a beat called a VEB by the reference annotator and a normal beat by the test annotator). Programs such as wave¹³can be used to search for and display the waveforms associated with the mismatches. To generate an output annotation file, add the -o option to the bxb command line, as in:

bxb -r 100 -a atr yow -L bxb.out sd.out -o

A particularly useful way to document an evaluation is to print a full disclosure report with bxb output annotations, using the program psfd (also included in the WFDB Software Package). This may be accomplished by preparing a file containing a list of the names of the records to be printed (call it list), and then using the command:

psfd -a bxb list >output.ps

The file output.ps can be printed on any PostScript printer. Run psfd without any arguments for a summary of its (numerous) options; try a short test before making a large set of printouts, which can take a long time.

Both bxb and rxr accept a -v option to run in “verbose” mode, in which each discrepancy is reported in the standard error output. When running rxr, this feature is useful for finding missed and falsely detected ectopic couplets and runs.

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Updated 10 June 2022