I think there are a few things at play here. I will not use the word big because that is so subjective. IMO:
(1) the criterion that determines whether a woman has a round booty or not is whether her bottom looks like the letter C. These women have a round/curvy no matter what their weight/clothing size.
- The level of what the "C" looks like varies between women, but it should be pronounced to a degree. Otherwise it's normal and not particularly round.
(2) women with who have wide hips and/or store most of their fat in their lower body with a curvature in at the waist are generally classified as pear-shaped women.
A woman can have just (1)+(2). Or just (1) without wide hips or much fat in the rest of her lower body. Or just (2) with a flat butt.
The studies mentioned in the first post lump all these women who have a curvier lower body together, however the results may not apply to all women equally.
- The first one is talking about women whose booties have more fat versus women with booties that have a "normal" level of fat.
- The second one is talking about women with wider hips (does not necessarily mean a large booty but depending on how this was measured booty size can contribute).
- And the last one is talking about women with larger butts/larger hips and smaller waists.