@staticmethod
def significant(pp, what):
    """Calculate significant expressed genes."""
    if what == 'gene':
        df_significant = pp.genes_detected[pp.genes_detected.loc[:, (pp.
            comparisons)].any(axis=1)]
    elif what == 'isoform':
        df_significant = pp.isoforms_detected[pp.isoforms_detected.loc[:, (
            pp.comparisons)].any(axis=1)]
    else:
        raise Exception('what= not known')
    return df_significant
