I wouldn't attribute this entirely to "my kid vs not my kid". I live in a western country and it's typically lower socio-economic groups that split and recouple

I wouldn't attribute this entirely to "my kid vs not my kid". I live in a western country and it's typically lower socio-economic groups that split and recouple with really young kids (i.e <5). The most at-risk groups for violence in these early years tend to also have uncoupled parents who are constantly seeing new men. If you split these statistics through 10th percentile socioeconomic groups I'm sure it wouldn't be as significant as 120 times. This paper is 10 years old and references Sweden as having less than a 10x increase.