When you get up in the morning and think about your job that you dislike, you would really prefer to stay in bed so you call in sick. this shows how can affect behavior?

Chen's research team randomly assigned some newborns and their mothers either to a breastfeeding promotion group (where breastfeeding was encouraged, but not required) or to a normal pediatric care group (where breastfeeding was neither encouraged nor discouraged). which research method did they use?