The researchers wanted to figure out the most suitable rents for houses in the Netherlands. They found a way to estimate these "market rents" based on how many people were interested in renting a place at a given price. If lots of people wanted a house at a certain rent, they thought that rent could be too low compared to what most people would pay (market rent). They used factors like house value, quality, and time on the market to calculate these market rents. By doing this, they could adjust rents to make sure houses didn't stay empty (keeping a 5% chance of not being rented). The study looked at different areas in the Netherlands and compared their calculated market rents to existing ones based on housing costs.