In Germany, a daycare allocation algorithm is separating siblings

To allocate this year's limited number of daycare slots, the city of Münster used an algorithm with a known limitation: it did not direct siblings to the same school. Parents were not pleased.


28 March 2023

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Last fall, the city of Münster introduced a new algorithm to allocate daycare slots. Parents were promised  more transparency when their children were not offered a place in daycare. But a few weeks later, the software was decommissioned after a string of problems. 144 children who were initially accepted lost their slots. 

Ann-Christine Spatzier, a parent representative for Münster's Youth Welfare Council, says that “parents want to get loud."  "We know that many children will fall by the wayside, that is what makes the whole thing so dramatic," Spatzier adds. "And now that there are not enough daycare staff, there are even less spots."

Because many German cities don't have enough daycare spots for all toddlers (preschool is not mandatory in Germany), cities usually develop a list of criteria to prioritize children from single-parent or low-income households. But these criteria are rarely followed in practice.

In February 2022, Münster's "Kita-Navigator" software was updated with an algorithm that allocated one offer per child. Parents and daycare managers - already on edge about staff shortages - immediately noticed that siblings were not being accepted into the same daycares (according to the city’s criteria, daycares should give priority to siblings of children who are already in.) They complained to the youth welfare office, which stopped the system. Another programming mistake mismatched the hours parents asked for with the hours they were offered.

"It's like a big wave spilling over at the moment… I don’t think the city expected this," Spatzier says. She has contact with the youth welfare office: "My sense is that the city was surprised and shocked about this mistake in the system."

Thilo Klein - an economist at the Leibniz Centre for European Economic Research, who helped develop the daycare allocation algorithm KitaMatch used in the neighboring district of Steinfurt - warns that a backlash against Münster could set a “frightening example” for other cities who want to change the current opaque system for allocating daycare slots, for example by introducing matching algorithms. 

Münster's daycare application software provider used an off-the-shelf algorithm that was openly known to not be able to match siblings to the same preschool. In fact, according to Thilo Klein, it is "a known problem" that the so-called Gale-Shapley algorithm cannot match pairs (e.g. siblings) into the same institution. In the United States in the 1980s, for example, when the algorithm was used to match trainee doctors with hospitals, it was unable to match married couples with the same hospital. 

Past problems 

In 2017, an administrative court in Münster ruled in favor of a family who sued the city for a daycare spot. The city had not been able to prove, for the state-run daycares, that all the children who were offered a spot were also those who would have had priority according to the city's criteria (such as children from low-income families, or single-parent households.)

Ute Doehnert, the manager of Kita Kotenbeis, a small English-language, parent-run daycare in the city center received 135 applications for seven spots this year. She had high hopes for the algorithm: "In the past years, we frequently had parents who were completely desperate, saying that their neighbor got five offers from daycares and they got none." 

Before the algorithm, rejected parents had to wait for families with five acceptance letters to cancel their four extra slots, and try again. Until all the daycare spots were filled, Spatzier said, "it would take months. And in the end, people who didn't get a place would be left over."

The Gale-Shapley update

Many other cities in North Rhine-Westphalia also use the ITK-provided "Kita Navigator" software to process applications by parents. In recent years, ITK has responded to pressure for a more transparent, faster and criteria-just allocation system by offering cities to update the software with the Gale-Shapley algorithm. 

The city of Marl also used the Gale-Shapley update this year. Here, the youth welfare office says that the update allows daycares to prioritize siblings of kids already in. However, ITK told them in advance that the algorithm could not match siblings applying together (e.g. twins). “We decided to reserve some places, so that these siblings don’t get left behind”, one employee explains. 

In Paderborn, the youth welfare coordinator has told the press that she is very satisfied with the algorithm. "So far, there hasn't been an uproar by the parents," says Klein. "Or they didn't know why they didn't get the slot they wanted," he adds. 

Meanwhile, the city of Münster confirms that, “the current algorithm is not programmed to match siblings,” adding that if “siblings can get spots in different daycares, their chance of getting a place at all is higher.” Right now, the city is trying to figure out how to match twins into the same daycare. 

The KitaMatch algorithm used in Steinfurt solves the Gale-Shapley “couples problem”  because it proceeds in rounds, i.e. daycares can accommodate sibling preferences in each round. ITK rep Markus Dietz says “there is no difference between our algorithm and the KitaMatch software,” though he isn't certain. “I assume we had to stay with our software provider,” says Oliver Brand from the city of Münster, when asked why the city decided to use ITK's algorithm.

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