Individual assessments may rise or fall depending on the characteristics of the property. The purpose of mass appraisal is to value all property by the same standards at the same time to create an equitable distribution of the tax levy.
If the same amount of money is to be raised for the current year after a valuation update from the previous year, and each assessment has doubled, the tax rate would be cut in half. And vice versa, if each assessment decreased by 20%, and the same amount of money was to be raised, the tax rate would increase by 20%. Increases or decreases in assessed values to not cause a tax increase or decrease.