Picture an employee at a retail store who has been told, in plain company policy, that every birthday brings a small gift card and a greeting card hand-delivered by the manager on the day itself. Now picture the birthday arriving and passing with nothing. A few days later, the card shows up, maybe with a sheepish apology. No harm done, right? It is the kind of slip most of us would brush off in the moment, even while feeling a small sting.
A study published in PNAS set out to measure whether that small sting actually shows up in how people work. The researchers found that it does: employees who got their birthday gift late later took more than 50% more sick days and worked over two fewer hours in the following month.
The question hiding at the bottom of the scale
Plenty of research has examined how bad managers harm their teams. But most of it focuses on serious misconduct, things like harassment, bullying, overt rudeness, or behavior that borders on illegal. Much less is known about the opposite end of the scale. How small can a manager’s misstep be and still register in employee performance?
That is the gap Michal Hodor of Tel Aviv University’s Coller School of Management set out to address, along with colleague Liat Eldor and Peter Cappelli of the Wharton School at the University of Pennsylvania. The authors define mild mistreatment as a failure to treat employees with the basic respect expected under everyday social norms. Think eye-rolling, ignored emails, getting talked over in meetings. These behaviors are common, but they are notoriously hard to study because they are subjective and rarely recorded.
Self-reports create their own problems. If you ask workers when they felt insulted, you cannot easily separate the slight from the worker’s mood or performance. Worse, poor performance might be what prompted the insult in the first place, making it hard to know which came first.
Why a birthday card makes a useful measuring stick
The researchers found a setting that sidesteps many of these problems. A national retail chain with 252 stores has a formal, company-funded policy: every employee with at least a year of service gets a birthday gift card and a greeting card, hand-delivered by the store manager on their birthday. The company digitally logs the exact delivery date, so any delay is documented rather than self-reported.
A late delivery fits the definition of a very modest slight. It is minor, yet it violates a recognized social norm, which is why greeting card companies sell entire lines of “belated birthday” cards. To confirm employees would actually feel slighted, the team surveyed a representative sample of retail workers in the same country. About 74% said they would feel hurt or insulted if their birthday gift arrived late, and that feeling held even when they assumed the delay was simple forgetfulness or competing priorities.
The team also needed to rule out that managers were withholding gifts from poor performers on purpose. Surveys of managers and human resources staff pointed the other way: 100% of managers said they would not delay a gift to punish a low performer, and roughly 91% of HR professionals said delays were unlikely to reflect performance. The data backed this up. Delays were not linked to employee demographics, past performance, or store characteristics. They showed up more often early in the year, when managers face heavier workloads from inventory, vendor tasks, and strategic meetings, which suggests the lapses were accidental byproducts of a busy manager rather than targeted punishment.
How the comparison worked
To isolate the effect of a late gift, the researchers used an approach called difference-in-differences. The basic idea is to compare two groups over time. The control group consisted of employees who received their gift within a five-day window around their birthday. The treatment group consisted of those who got it later than that. The team then tracked two measures of work behavior month by month: actual working hours and paid sick days.
A key check is whether the two groups behaved similarly before the birthday. If they did, any divergence afterward can more confidently be tied to the late gift. The analysis found no meaningful differences in the months leading up to the birthday, which supports the idea that employees were genuinely surprised by the delay and that struggling workers were not being singled out. The study drew on data from 2018 and 2019 covering 8,722 eligible employees.
The results pointed in a consistent direction. In the month after a missed birthday, working hours dropped by more than two per month, about a 1.5% decline, while sick days rose by more than 50% relative to the period just before the birthday. The reduction in hours likely reflects small acts of withdrawal that add up: arriving a little late, leaving a little early, taking longer breaks.
The effect did not last. By two months after the birthday, both working hours and sick days returned to their earlier levels. The authors suggest the late gift may function as a kind of apology that repairs the relationship, or that employees simply move on. They note they cannot fully distinguish between those explanations.
Hurt feelings, not lost cash
Why would a forgotten card change anyone’s behavior? The researchers tested two possibilities. One is an emotional response, a sense of being overlooked or treated unfairly. The other is purely financial, since the gift card carries real money.
The evidence leaned toward emotion. The reaction was concentrated among middle-level managers within the stores, the employees who supervise front-line staff. The team interprets this through prior research suggesting that higher-status workers expect a stronger relationship with their bosses and feel a sharper sting when that expectation is broken. Their drop in hours and rise in absences was more than double the overall average, while front-line employees reacted far less.
The financial explanation got little support. Gift values rose with tenure, ranging from about $57 to $350. If money were driving the response, employees with larger gifts should have reacted more strongly. Instead, the bigger increase in sick days came from lower-tenure employees receiving the smallest gifts, worth roughly 2% of monthly pay. That pattern points to the slight itself, not the dollar amount, as the trigger.
The team also found that expectations matter over time. Among workers observed in both years, those who got their gift on time in 2018 but late in 2019 showed an especially strong reaction, a drop of more than four working hours and a rise in sick days above 45%. The authors read this as evidence that a broken expectation, rather than the event in isolation, drives the response.
What it might mean for workplaces
The researchers translate the absence effect into money for the chain: an estimated $129,600 per year in lost sales and replacement costs, based on the rise in sick days. They caution that this is a rough calculation built on the chain’s specific economics, not a universal figure.
Their broader takeaway is that organizations should not dismiss small interpersonal lapses as harmless, and that interpersonal skill deserves a place in how managers are selected and evaluated. At the same time, they argue the burden should not fall on individual managers alone. Because delays tended to cluster when managers were stretched thin, the authors suggest that workload and operational pressure are part of the story, and that balancing profit-focused demands against people-management duties is an organizational responsibility.
A few caveats are worth keeping in mind. The data come from a single retail chain in one country, the working-hours measure is aggregated monthly rather than tracked day by day, and the effects faded within a couple of months. The study also did not find a link between late gifts and employees quitting. What it offers is evidence that even a slight most of us would shrug off can leave a measurable, if temporary, mark on how people show up for work.
