Like parent like child

A 1998 CDC study finds a correlation between adults who complain about various problems, and adults who also complain about childhood problems:

A strong relationship was seen between the number of adverse experiences and self-reports of cigarette smoking, obesity, physical inactivity, alcoholism, drug abuse, depression, suicide attempts, sexual promiscuity, and sexually transmitted diseases. Furthermore, persons who reported higher numbers of adverse childhood experiences were much more likely to have multiple health risk behaviors. Similarly, the more adverse childhood experiences reported, the more likely the person was to have heart disease, cancer, stroke, diabetes, skeletal fractures, liver disease, and poor self-rated health as an adult.

So here is the faulty causation conclusion:

"Abused children may use behaviors such as cigarette smoking, heavy alcohol use, overeating, promiscuity, and drug use as a way of coping with damaging experiences much earlier in life, "says a principal investigator of the study, Dr. Vincent Felitti, Chief of Preventive Medicine at Kaiser Permanente in San Diego.

Maybe, but there are many more likely possibilities as well. Maybe the complainers are not really any worse off; they just like to complain. The same people who like to complain about adult problems are likely to complain about childhood problems. Maybe also the problems are genetic, cultural, or socio-economic. Maybe the bad behavior is causing the abuse, instead of the abuse causing the bad behavior. There are so many possibilities that a study like this is worthless.