A fairly lengthy article about cervical cancer might not sound the most interesting way to spend ten minutes but it provides a good example of epidemiology confusing cause and effect.
Velvet Glove, Iron Fist
October 8, 2010
In 1842, the Italian physician Domenico Antonio Rigoni-Stern noticed that nuns in Verona were more susceptible to breast cancer than other women. Ruminating on what aspect of convent living might explain the phenomenon, he concluded that the nuns’ corsets were too tight. This explanation was wide of the mark but the initial observation was sound; we now know that having children makes a woman less likely to develop breast cancer.
But the Italian found another association. It seemed that the nuns were less prone to cervical cancer than the rest of society. Furthermore, cervical cancer was unusually common amongst prostitutes. This observation provided the first clue to the real cause of the disease but it would take a further century and a half of confusion and dead-ends before the real truth emerged.