The findings confirm reports of a spike in the birth rate, although they fall far short of the 45% increase reported by some media at the time.

The researchers say their results suggest that "human emotions on a large scale can profoundly affect demographic swings in populations" and "could contribute to a better understanding of human behaviour, improve healthcare planning, and even aid government policy makers in stimulating or reducing birth rates."

On 6 May 2009, Andrés Iniesta scored a last minute goal against Chelsea FC, which put Football Club Barcelona in the UEFA Champions League final. Nine months later, Catalonia's local radio station broadcast the results of an informal survey of five hospitals, showing a 45% increase in the number of births.

The children born during this boom were dubbed "the Iniesta generation."

Similar claims have been made in the past, but have since been disproved. For example, the New York Times reported a 30% increase in births at five Manhattan hospitals after the 1965 blackout.

A team of health and statistical researchers in Catalonia wondered if the Iniesta effect in Catalonia was real, and, if so, whether the exhilaration associated with football or other sporting events can truly have profound demographic repercussions.

So they analysed monthly birth data over five years (2007-2011) including 11,000 births at two maternity centres in the Catalan counties of Bages and Solsones, which have a combined population of about 190,000 and include the town of Santpedor -- the birthplace of Josep Guardiola, FC Barcelona's coach from 2008 to 2012.

After adjusting for several factors, they found a significant (16%) increase in births in February 2010, nine months after FC Barcelona's exciting victories, and an 11% increase in March compared with other years.

This study confirms media reports of an increase in births nine months after FC Barcelona's extraordinary sporting successes in May 2009, say the authors. However, the results fall far short of the reported 45%. They also suggest that the term "Iniesta generation" is a misnomer.

The results also show a decline in births from the second half of 2010, which the authors suspect may be caused by the Spanish economic crisis and a decline in planned births.

"In summary, our results may have several different interpretations," say the authors. "One is that human emotions on a large scale can profoundly affect demographic swings in populations, that national or regional events can reduce the weight of reason and increase the weight of passion.

Validation of our results could contribute to a better understanding of human behaviour, improve healthcare planning, and even aid government policy makers in stimulating or reducing birth rates," they conclude. However, one should always be cautious in interpreting the results of an observational study.

"Ideally, to bridge the gap between observational and trial data, it would help greatly if Iniesta were willing to replicate his intervention -- although the cost of such a study could be prohibitive, not to mention harmful to the reference group (Chelsea)," they add.

Editor's Note: The British Medical Journal traditionally publishes a Christmas issue containing a number of articles of a lighthearted nature. For a full list of articles in the 2013 issue, see: http://www.bmj.com/content/347/7938