Eaton broke his own decathlon world record at the world championships in Beijing in August.
The 27 year old also won world gold in Moscow in 2013, a year after clinching Olympic gold in London.
Eaton took the award despite sprint superstar Usain Bolt clinching a fifth treble gold showing in a major championship in Beijing.
The Jamaican star had performed the same feat at the 2008 and 2012 Olympics in Beijing and London, and world championships in 2009 and 2013 in Berlin and Moscow.
Dibaba, 24, is the current world record holder in the women's 1500m and holds three further world records indoors.
The IAAF normally holds a star-studded season-ending awards gala in Monaco but that was canceled this year following allegations of corruption at the highest echelons of world track and field's governing body.

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