The Birthday Effect: True Statistic or Data Malfunction?

The fascinating phenomenon known as the birthday effect, or the birthday blues, has long fascinated mathematicians, statisticians and the general public. It refers to the statistically significant increase in the probability of death occurring on a birthday, compared to other days of the year.

This odd occurrence has been the subject of various studies, raising questions about its validity and the underlying causes. While some see it as a curious statistical anomaly, others wonder if there are deeper psychological reasons behind this seemingly morbid coincidence.

Is there a genuine birthday death risk? Before we change the words to Happy Birthday, let’s attempt to shed some light on what’s known as the birthday effect.

For Renaissance painter Raphael, legendary wordsmith William Shakespeare, Golden Era great Ingrid Bergman, explorer Lawrence Oates, civil rights activist Ella Baker, and scientist George Washington Carver, the answer is yes. They all died on their birthdays, but is there any substantive evidence to suggest the birthday effect is authentic? It seems there is.

2012: Switzerland

Perhaps the most well-known study, published in the Annals of Epidemiology, was carried out in Switzerland in 2012. Led by Dr. Vladeta Ajdacic-Gross from the University of Zurich, the study investigated the validity of the birthday effect by analysing the mortality data of just under 2.4 million people aged one and over who died between 1969 and 2008.

The team of researchers attempted to find out whether people are more likely to die on their birthdays compared to other days of the year. Using a large dataset of mortality records, the study provided solid statistical evidence on this phenomenon.

The findings revealed a significant 13.8% increase in the likelihood of death occurring on a birthday. This heightened risk was particularly pronounced among older adults and those suffering from cardiovascular diseases and strokes. The study also suggested that psychological stress associated with birthdays, along with things like overindulgence in food and alcohol, might contribute to the increased risk.

The researchers concluded that the birthday effect is a genuine statistical phenomenon, driven by a combination of psychological and physiological factors.

2015: United States of America

A similar study in the USA which analysed the Social Security records of 25 million people who died between 1998 and 2011 also lent weight to the suggestion that there’s a greater risk of dying on your birthday, to the tune of 6.7%.

Like the Swiss study, this one, led by Pablo Peña, an economist at the University of Chicago, confirmed a statistically significant increase in mortality on birthdays, especially among older adults. The researchers found that the risk was higher for deaths related to cardiovascular diseases and suicides. They proposed that the stress and emotional strain associated with birthdays – sometimes known as the birthday blues – combined with potential risky behaviours such as overeating or excessive drinking, might exacerbate underlying health conditions, leading to a higher likelihood of fatal events.

2016: Japan

A 2016 study of almost 2.1 million Japanese who died from ‘major external causes’ between 1974 and 2014 revealed a noticeable increase in the birthday death risk, particularly among the elderly. Tetsuya Matsubayashi, professor at the Osaka School of International Public Policy at Osaka University, and Michiko Ueda-Ballmer, associate professor at the Maxwell School of Citizenship and Public Affairs at New York’s Syracuse University, showed that people were more likely to die on their birthday than on any other calendar day by traffic accidents, other accidents, drowning, and choking. For suicide cases in particular, people were 50% more likely to die on their birthday compared to any other dates.

According to these studies, the answer to the question ‘is the birthday effect real’ is a resounding yes, but not everyone agrees.

Despite the compelling statistical evidence, the birthday effect remains a topic of much debate. Some researchers argue that there’s no greater risk of dying on your birthday than any other day of the year and that the observed patterns could be due to data artefacts (the way data is collected, processed, or analysed) or other variables that haven’t been accounted for in the studies.

A 1999 study of just over two million deaths in Austria and Denmark by Gabriele Doblhammer, Professor of Empirical Methods in Social Science and Demography at the University of Rostock in Germany found that there was no evidence of the so-called birthday effect.

The same goes for a German study of cancer deaths between 1995 and 2009, and in a study of mortality data from England and Wales in the 1970s, it reported a small statistical anomaly in subgroups but not in the population as a whole.

Several theories have been proposed to explain the unnerving phenomenon of increased deaths on birthdays, commonly referred to as the birthday effect. These theories include:

Psychological Stress

Birthdays can be emotionally stressful, especially for older adults who can become torn between celebrating another year of life, and the unstoppable march of time. In addition, physiological stress responses, such as increased blood pressure and heart rate, can exacerbate underlying health conditions, leading to fatal events. There’s also the theory that the birthday blues – born from feelings of depression, loneliness, unmet expectations, for example – can sometimes lead to an increase in suicide on birthdays, as the Japanese study noted.

Self-Induced Behaviour

Birthdays often involve celebrations that can include excessive eating, binge drinking, and poor decision making. These activities can strain the body, particularly in individuals with pre-existing health issues, increasing the likelihood of death. In America, the drinking age is 21 and there’s data to suggest a significant spike in mortality rates on the 21st birthday and the following day, primarily due to an increase in accidents.

Medical Neglect

Some have speculated that people may delay seeking medical attention or treatment around their birthdays, either because they want to enjoy the day or, perhaps due to psychological denial, potentially worsening health conditions which can lead to higher death rates.

End-of-Life Timing

Another speculative theory is that people might psychologically or subconsciously ‘hold on’ to reach their birthday before succumbing to their illnesses, resulting in a spike in deaths on the actual day.

Each of these theories attempts to account for the birthday effect, suggesting a complex interplay of psychological, behavioural, medical, and physiological factors.

Is the birthday effect real? It’s hard to know with any degree of certainty, or at least without far more data, and it remains a compelling and somewhat unsettling phenomenon.

On one hand, the phenomenon of the birthday effect is supported by numerous studies across various countries where the consistency of findings suggests a genuine statistical pattern, yet there remain alternative views which attribute the observed increase in mortality rates on birthdays to data artefacts.

Further research is needed to further unravel the complexities of the birthday effect and to understand the complex connections between psychological and physiological factors which may contribute to the increased risk of death on your birthday.