The property may be reassessed under certain conditions other than a change of ownership, such as when additions or new construction occur. The assessed value is also subject to reduction if the market value of the property declines below its assessed value, for example, during a real estate slump. Reductions of property valuation were not provided for by Proposition 13 itself, but were made possible by the passage of Proposition 8 (Senate Constitutional Amendment No. 67) during 1978 that amended Proposition 13. Such a real estate slump and downward reassessments occurred during 2009 when the California State Board of Equalization announced an estimated reduction of property tax base year values due to negative inflation. The property tax in California is an Ad valorem tax meaning that the tax assessed (generally) increases and decreases with the value of the property.