Generally, DHS surveys are not fielded in the same PSUs between survey years. This is the case in Bolivia, so unfortunately you cannot compare results over time at the cluster level. You may compare results at the representative region level for the surveys, although those boundaries changed slightly between these surveys: see http://spatialdata.dhsprogram.com/boundaries/#view=map&c ountryId=BO&surveyId=319%2C238&level=1%2C1 for a comparison.