text: Title: compare_intra() keeps giving 'index X is out of bounds for axis 0 with size Y' error
  Body: Tried `compare_intra()` on a road accident data set to compare urban vs rural samples. However, it keeps giving the above error.
  
  `report = sv.compare_intra(df, df["UrbanRural"] == 1, ["Urban", "Rural"], 'Is Fatal')`
  
  Removed from `df` up to four fields that the error is reported on, but then the next field throws the error. Unfortunately, the data set is private so can't share, but could this be an issue with the code itself?