This means the data is subject to differing degrees of sampling variability, i.e., the true value for any measure lies in a differing range about the estimated value.
Gan fod y data'n dod o arolwg, mae'r canlyniadau'n amcangyfrifon wedi'u seilio ar samplau ac felly'n destun graddau gwahanol o amrywioldeb samplu, h.y.