def METHOD_NAME(self):
    """
    Fit the cross section to the selected element/charge state,
    using the specified model on the chosen temperature interval.
    """
    species = self.getElement()
    Z0 = self.getZ0()
    T_lower = self.getTlower()
    T_upper = self.getTupper()
    if T_lower >= T_upper:
        QMessageBox.critical(self,
            "Invalid temperature range selected",
            "The lower temperature cut-off must be strictly less than the upper temperature cut-off.")
        return
    idx = self.ui.cbMethod.currentIndex()
    if idx == 0:
        method = 'single'
    elif idx == 1:
        method = 'single3p'
    elif idx == 2:
        method = 'double'
    else:
        QMessageBox.critical(self,
            "Unrecognized fitting method",
            "Unrecognized fitting method selected: '{}'.".format(self.ui.cbMethod.currentText()))
    _, _, params = ADAS.fit.fitKineticIonizationForSpecies(species, Z0=Z0, fittype=method, T_lower=T_lower, T_upper=T_upper)
    self.drawFit(params)
    self.showParams(params)