Berlin. Management had tried everything. In order to reduce the high level of sickness in their supermarket chain, management introduced compulsory medical certificates from day one. It stipulated that employees could no longer simply call in sick via text message, but had to call their superiors personally. She brought coaches into the company as contact persons for employees who were often absent due to psychological stress.
None of that helped. In none of the retailer's 16 branches did sickness rates fall sustainably. Until management turned to Timo Vogelsang, professor at the Frankfurt School of Finance and Management. Vogelsang then conducted an experiment with the company. Within a few months, he reduced the probability of employees calling in sick for a day by 44 percentage points. How did he do that?
For this reason, Vogelsang targeted one-day absences: “The probability that someone will give up is likely to be higher for one-day absences than for multi-day absences.” The expert lists a few classic cases: Salespeople who don't want the unpopular Saturday service. Project employees who have a particularly unpleasant customer meeting coming up. Or simply employees who have a hangover from the night before.
What is important to the researcher is that companies should under no circumstances force sick employees to work. “Our express goal in the experiment was to only reduce days of absence that were not due to illness – i.e. classic ‘blue-collar’ days.” The problem: It is impossible to determine with certainty whether an employee who has reported sick is not actually sick.
Vogelsang approached a solution like this: In his experiment, he only focused on a quarter of all supermarket employees - namely the 25 percent who were most often absent from work for short periods of time while sick during the survey period. Vogelsang did not include long-term sick employees.
In the supermarket chain, these “frontrunners” among short-term sick people were then sent a letter home as part of the experiment, signed by their employer. This included neither accusations nor threats of punishment. In addition to health promotion offers, the company only listed two key figures. First: The “absence rate” of the respective employee in the measurement period. For example, anyone who had to complete 100 working days in a certain period of time and was on sick leave for five of those days had an absenteeism rate of five percent.
Secondly, and this was the researchers' crucial trick: they wrote to the employees how high the average absenteeism rate was in the company during the same period. For example, the supermarket employees then read in their respective letters: “For comparison: half of the company’s employees have an absenteeism rate of less than five percent.” The positive effect then occurred in the group of those contacted.
But why is this comparison with the rest of your colleagues so effective? “We took advantage of the fact that most people have the desire not to deviate from the crowd and to behave ‘normally’,” says scientist Vogelsang. If they were given a guideline of how often colleagues were sick on average, most of them used this as a guide. Anyone who previously called in sick on seven days out of a hundred would then prefer to go down to five days in order to get closer to the average.
This “desire for conformity” is usually so great that it is even more effective than financial incentives, says Timo Vogelsang. He had already published a study in 2024 with the research question: Can management reduce sick leave by paying bonuses for attendance? Result: no. “Such attendance bonuses can be a disincentive,” says the expert. “Employers unintentionally signal to their people that coming to work is worthy of a bonus – and therefore not the norm.”
Reducing the sickness rate with the help of a letter that does not contain any accusations, penalties or strict new rules: For many managers, the method that Timo Vogelsang has tried out here is likely to be a hope. But how easy is it to integrate them into everyday company life? And is it even legally compliant?
André Kasten is a specialist lawyer for labor law at the Berlin law firm Abeln. He says: A letter that simply informs the employees concerned about their absences, puts them in relation to the anonymized rest of the company and lists offers of support is initially not legally problematic. The letter would only be problematic if it created undue pressure on employees.
Kasten still sees some pitfalls for employers. The procedure would be subject to co-determination, says the lawyer. “This is because the letter aims to influence sick-calling behavior.” In labor law, this falls under the umbrella term of “collective behavior control”. In companies with a works council, this is only legally secure if there is a corresponding works agreement.
Employers also have to be careful when it comes to data protection. “Processing employee health data is generally only permitted with express, voluntary and informed consent,” says André Kasten. It is best for companies to obtain this declaration of consent from their employees in writing.
Kasten also points out that the letter to employees must in no way discriminate against those with chronic illnesses or disabilities. “This is particularly true if this exerts pressure or threatens follow-up action.” For employers who take all of this into account, the letter method is legally permissible and practical.
