Not surprising that premature babies have higher psychiatric risk

The authors of an article in Archives in General Psychiatry, linking prematurity and admission to psychiatric hospital, are reported by Reuters as saying that the "increased risk may be down to small but important differences in brain development". Just finding an association does not mean that there is necessarily a causal link. The association may be related to a third factor. For example, prematurity is associated with social class, as is psychiatric admission. Social class may be more of a causal factor producing both prematurity and psychiatric admission. 

Of course the researchers know this. In their paper, they say "the association between preterm birth and psychiatric outcomes may be confounded by risk factors, including unmeasured sociodemographic and lifestyle factors (including ethnicity and socioeconomic status) ...". However, the bias to place a biomedical, rather than social, interpretation on such results is illustrated by this example. The finding of an increase in psychiatric admissions in those with premature birth should not be surprising because of the link through social deprivation.