"This study does not enable us to choose between the two hypotheses, " she told BBC News.

BBC: Studying how snakes got legless

The researchers offer two hypotheses for this rise in grumpiness.

ECONOMIST: The science of justice

However, these concurrent changes could support either of two hypotheses: that crime rises when individuals own more guns, or that individuals purchase more guns to defend themselves against rising crime.

ECONOMIST: Economics focus

There are at least two hypotheses.

ECONOMIST: Animal behaviour

In his own study, Dr Austin tested 24 hypotheses, two for each astrological sign.

ECONOMIST: Why so much medical research is rot