The link between family income during childhood and the later risks of psychiatric disorders, drug addiction or violent crime has not yet been established.
In one study of a Finnish sample of 650 680 people, it was first found that increased family income was associated with lower odds of psychiatric disorders, substance abuse, and arrest for violent crime.
However, once the comparison was made between siblings from the same family but then exposed to different income levels, these correlations disappeared. The notion that poverty and crime are inextricably linked, is nevertheless a popular one imported from the US. It has been a convenient way of explaining away the role of ethnicity and cultural mores.
The links between family income and psychiatric disorders, substance abuse and felony arrest can therefore be explained by shared family risks and do not suggest a cause and effect link.
For every $15 000 increase in family income at age 15, the odds of developing serious mental illness were reduced by 9 percent and 23 percent for violent crime arrests. These associations were very blurred in the sibling comparison models however and deeper analyzes confirmed these latter results.
The study was aimed at understanding whether childhood family income predicts subsequent violent crime and drug addiction and whether the associations are in turn explained by unobserved family risk factors. In Sweden, low family socioeconomic status is a known indicator of criminal and substance abuse behaviors in adulthood, but the causal relationship is questionable.
The Swedish national study on family units born between 1989 and 1993 between 15 and 21 years, showed that children of parents in the lowest income quintile have a seven times higher probability (HR) of being convicted of violent crime compared to their counterparts in the highest quintile. This link was greatly attenuated when taking into account unobserved family risk factors .
The study highlighted that there was no association between family income and subsequent violent crime or drug addiction once unobserved family risk factors were taken into account.