Please note: The algorithm descriptions in English have been automatically translated. Errors may have been introduced in this process. For the original descriptions, go to the Dutch version of the Algorithm Register.
WOZ valuation with model-based valuation
- Publication category
- Impactful algorithms
- Impact assessment
- Field not filled in.
- Status
- In use
General information
Theme
Begin date
Contact information
Link to publication website
Responsible use
Goal and impact
Every year we determine the WOZ value of all houses in Nijmegen. To carry out this process, we use a calculation model (the algorithm). This allows us to do the work better and faster. It also ensures that we treat all homes in the same way.
The algorithm affects the owners of homes, as the WOZ value determines how much property tax someone has to pay for their home. It also affects income tax and landlord tax. For tenants, the WOZ value can affect the maximum rent. This is because the WOZ value is part of the point system used to calculate the maximum rent.
Considerations
The alternative to this algorithm is to calculate the value completely by hand. Due to the large number of properties, this takes a lot of time. It also increases the risk of errors. It is better to use the algorithm because it ensures less manual work. With that, we have more time for checks. It is also important to treat equal cases equally. This is better done by following a standard process, which we can automate. This way, we ensure that the burden is shared fairly among residents.
Human intervention
The data the algorithm will calculate with are from sold houses. We check this data before calculating with it. We check whether the properties are correct. This includes the following data: parts of the house such as the usable area, additions, dormers and garages. We also use information about the condition of the property: such as how well it has been maintained, the quality of amenities like kitchen and bathroom and the quality of the property itself.
After the algorithm calculates a value, our appraiser checks it. The appraiser checks the value with sales figures of homes that are comparable. And it is checked against the previous year's objections. The Valuation Chamber (the national regulator) also regularly checks our work and that of other municipalities.
Risk management
Key risks are: the quality of data on houses, the quantity of houses sold, the design of the model and the quality of checking the results of the calculation model.
The various data must be reliable to calculate the correct results. We mitigate this risk through human control at different points in the process. The Valuation Chamber does an external check on the calculation of our WOZ values and has to give permission before we can set final WOZ values.
It is also important that we can properly explain the results of the calculation model. We can do this because we know how the values are calculated. You can view the assessment report via the municipality's website for a substantiation of the value of your property.
Legal basis
The Property Valuation Act (WOZ). This act aims to regulate the determination of these values.
Links to legal bases
Link to Processing Index
Operations
Data
When calculating the WOZ values, we use various basic registrations: In these, the Dutch government keeps various data. Data on who owns a property and how big the plot is come from the Basic Land Registry. We also use the Addresses and Buildings Key Register. This provides data such as the surface area of the house and the year of construction. For the WOZ Act itself we collect the following data: components of the property such as the usable area, additions, dormers and garages. We also collect data on the condition of the property such as the level of quality, maintenance and amenities. We collect this data via data from sales advertisements, purchase enquiry forms and information forms.
Technical design
The algorithm calculates with said information of sold properties and, based on this, calculates a WOZ value for sold and unsold properties. The WOZ values are always still checked by one of our appraisers and adjusted if necessary.
External provider
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