diff --git a/mlair/plotting/postprocessing_plotting.py b/mlair/plotting/postprocessing_plotting.py
index c7647ef5bf5b5b6c46eae9318c0fd99b294292c6..9843728c62e8b745a2cf1e941af0801d6e9ab0d7 100644
--- a/mlair/plotting/postprocessing_plotting.py
+++ b/mlair/plotting/postprocessing_plotting.py
@@ -17,7 +17,6 @@ import seaborn as sns
 import xarray as xr
 from matplotlib.backends.backend_pdf import PdfPages
 from matplotlib.offsetbox import AnchoredText
-from scipy.stats import mannwhitneyu
 
 from mlair import helpers
 from mlair.data_handler.iterator import DataCollection
@@ -753,12 +752,6 @@ class PlotFeatureImportanceSkillScore(AbstractPlotClass):  # pragma: no cover
         self._number_of_bootstraps = np.unique(data.coords[self._boot_dim].values).shape[0]
         return data.to_dataframe("data").reset_index(level=np.arange(len(data.dims)).tolist()).dropna()
 
-    @staticmethod
-    def _get_target_sampling(sampling, pos):
-        sampling = (sampling, sampling) if isinstance(sampling, str) else sampling
-        sampling_letter = {"hourly": "H", "daily": "d"}.get(sampling[pos], "")
-        return sampling, sampling_letter
-
     def _return_vars_without_number_tag(self, values, split_by, keep, as_unique=False):
         arr = np.array([v.split(split_by) for v in values])
         num = arr[:, 0]