Problem to be Solved;To select a marker peak which characterizes a difference between groups, even when the number of samples belonging to each group is small.;Solution;A peak matrix is created based on the peaks detected from mass spectra of a plurality of samples belonging to a plurality of groups (S1-S3). Each row of the peak matrix represents a peak-intensity distribution for a large number of samples at one mass-to-charge-ratio value. If there is no difference between the groups at a certain mass-to-charge-ratio value, the peak-intensity distribution at that mass-to-charge-ratio value should be a lognormal distribution (or normal distribution). Accordingly, a hypothesis test for the conformity of the peak-intensity distribution to the lognormal distribution is performed for each mass-to-charge-ratio value (S5). A mass-to-charge-ratio value at which a significant difference has been found is selected as a candidate of the marker peak (S6).
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