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 8 March 2019