If you select for some characteristic, and find that groups differ on other characteristics, it is natural to assume that the variable you selected might be causal. For example, if you select on the basis of genetics, and find differences, it would be understandable if you thought that genetics accounted for the other differences. Equally, if you select on wealth, it would be natural to imagine that any differences you find were due to differences in wealth.
Norway is a special case. It is very rich, and very Norwegian. No-one does fiords like they do. Norwegians are dying out, their total fertility below replacement, so they are of only historical interest, but serve to illustrate what a very rich country can provide its citizens in terms of very high-quality universal health care, and a sovereign wealth fund which hold 1.7% of the world’s wealth, equal to £175,000 (\$245,000) per citizen. Even poor Norwegians are extremely rich by global standards, and Norway tops the world in the Human Development Index. Most countries would have to create and save wealth for a century to reach the levels of poor Norwegians.
75% of citizens are genetic Norwegians, and the rest came in over “recent decades” which is a bit vague, but which makes sense for anyone able to look at Human Development statistics. Norwegians like collecting data, for which we should be grateful.
Parental income and mental disorders in children and adolescents: prospective register-based study
Jonas Minet Kinge, Simon Øverland, Martin Flatø, Joseph Dieleman, Ole Røgeberg, Maria Christine Magnus, Miriam Evensen, Martin Tesli, Anders Skrondal, Camilla Stoltenberg … Show more
International Journal of Epidemiology, dyab066, https://doi.org/10.1093/ije/dyab066
In this registry-based study of all children in Norway (n = 1 354 393) aged 5–17 years from 2008 to 2016, we examined whether parental income was associated with childhood diagnoses of mental disorders identified through national registries from primary healthcare, hospitalizations and specialist outpatient services.
There were substantial differences in mental disorders by parental income, except for eating disorders in girls. In the bottom 1% of parental income, 16.9% of boys had a mental disorder compared with 4.1% in the top 1%. Among girls, there were 14.2% in the lowest, compared with 3.2% in the highest parental-income percentile. Differences were mainly attributable to attention-deficit hyperactivity disorder in boys and anxiety and depression in girls. There were more mental disorders in children whose parents had mental disorders or low education, or lived in separate households. Still, parental income remained associated with children’s mental disorders after accounting for parents’ mental disorders and other factors, and associations were also present among adopted children.
Mental disorders were 3- to 4-fold more prevalent in children with parents in the lowest compared with the highest income percentiles. Parents’ own mental disorders, other socio-demographic factors and genetic confounding did not fully explain these associations.
The authors analysed immigrants separately, and excluded those with incomes in the bottom 2% as well. They could also look at adopted children, which was a useful way at looking at genetic factors. They had full data on actual earnings, and calculated family income as the after tax earnings of both spouses, adjusted for inflation. They had health data from official sources, so this study gets round all the problems of self-report. It is also a full representation of massive population size, which puts most other studies in the shade.
Poorer families had more disturbed children. Boys were more disturbed than girls.
However, boys seem to stabilize as they grow older.
Boys are very prone to attention-deficit hyperactivity.
Single parents, parents without degrees, and parents with mental disorder, have disordered children.
Higher parental income was associated with lower prevalence of children’s mental disorders, also in the international adoptee subgroup, although with a less pronounced association, compared with the Norwegian-born. For every decile increase in parental income, there were 0.25% fewer adoptees diagnosed with mental disorders compared with 0.66% fewer per decile in Norwegian-born children. Except for eating disorders, international adoptees had ∼1.5–2 times higher prevalence of any mental disorders compared with Norwegian-born children.
So, adoptees from abroad were more mentally disturbed, but less influenced by Norwegian wealth differences.
Three major conclusions can be drawn from this study. First, despite relatively equal access to health services, childhood mental disorders were found to decrease continuously with parental income and there was no dividing line above or below which additional income was no longer associated with mental disorders. The associations varied with child age and sex. Second, the association with parental income was present for all mental disorders except eating disorders and largest for ADHD. Third, the association of parental income with mental disorders could partly, but not fully, be attributed to parental mental disorder and socio-demographic factors. In addition, the associations were present, but less pronounced, in children genetically unrelated to their parents.
The influence of a genetic component is also suggested. Children of parents with mental illness are at a higher genetic and environmental risk of developing psychopathology. Low income can be a consequence of psychopathology in parents. The largest income difference was found for ADHD, a mental disorder with a strong heritable component, which is also associated with reduced income in adulthood. In contrast, the difference across the income spectrum was smaller for anxiety, which has been shown to have a large environmental component. These differences suggest confounding by underlying genetic susceptibility on the relationship between parental income and offspring mental disorders. In addition, the associations between parental income and mental disorders in adopted children were weaker compared with children living with their biological parents. The differences in the associations with parental income observed among adopted children and Norwegian-born children were also greater for ADHD than for anxiety disorders.
No intelligence test data seem to have been available, which is a pity. No DNA either, but that could be collected now, to greatly increase our understanding of genetic contributions. I have described the effects as due to wealth, but the measure actually collected was parental income. That usually translates into wealth, but strictly speaking what is being studied is the family income as children are being brought up, which may be the most important thing.
The results show some apparent effects of wealth differences, even when controlling for education. The authors speculate that the effects of income differences might be bigger in other countries. Perhaps so, but I think that the real message is that most countries will never be as rich as Norway, and even in Norway, when family income is used as an indicator, there are differences in children’s mental states which are probably nothing to do with poverty as such.