One of the participants, an Atlanta radio talk-show host, said lots of moms call her show to testify that deciding to stay home with their kids was the best decision they ever made. They are personal. Belsky is doing social science, not personal science. His results, as he would admit, do not necessarily predict individual outcomes. Nonetheless, there's still that matter of common sense.
Common sense says day care is going to breed more aggressive behavior than home care.
The fact is, Belsky's findings line up fairly well with common sense. Furthermore, his data is supported by other findings. For example, as the number of young children in full-time day care has increased, so have the incidence and severity of child behavior problems. That doesn't mean day care is causing all those problems. It certainly isn't, but it's undoubtedly playing a role.