Let us enter into theoretical lala land for a moment.

Pretend we discover that there is no direct physical mechanic of which causes lung cancer (smoking directly affects lung tissue because smoke on lung tissue = instant mutation), but it is the belief tied to the object that causes lung cancer (believing in smoking causes lung cancer causes the brain to release a different proportion of chemicals which are correlated with depression, which creates alterations in their physical health, which affects their entire organic environment, which unlocks a gene that makes a person genetically predisposed to getting cancer more likely to get cancer). Assume for the sake of absurdity, that that is the direct causal mechanic and it works predictably and repeatedly 100% of the time, just like gravity.

Now that particular hypothetical is probably completely ridiculous, but for complex societal systems, it absolutely is not. How people observe and treat single parents based on the data they know about them affects the entire system as well. Complex sociological issues are nearly impossible to study without introducing bias and influence into the behavior of the system. If all single parents who are studied are very angry at being single parents, and they can not resolve this, then that might suggest something about the child's home life. And that also suggests something about every parent that comes into a clinic for a study. And you really don't know whether it's because people infer that A is a single parent, or people know with certainty that A is a single parent, because in real world social systems, people label other people using tons of correlative markers to identify 'types' of people. And you really don't know whether people treat A in such and such a way, because they read a study, or because they developed personal bias through interpersonal experience. Most of the world is online today, and are capable of quickly scanning popsci articles posted on facebook.