An extraction apparatus generates a plurality of Betti series based on Betti numbers obtained by performing a persistent homology transform on a plurality of pseudo-attractors generated from a plurality of pieces of time-series data. The extraction apparatus generates a plurality of transformed Betti series in which a region with a larger radius at the time of generating the Betti numbers is weighted more than a region with a smaller radius from the plurality of Betti series. The extraction apparatus extracts abnormality candidates from the plurality of pieces of time-series data based on the Betti number in the plurality of transformed Betti series.
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