sentences:  A re-analysis of the 2009 study found that the paternal age effect could be explained by adjusting for maternal education and number of siblings.A 2012 Scottish study found no significant association between paternal age and intelligence, after adjusting what was initially an inverse-U association for both parental education and socioeconomic status as well as number of siblings.A 2013 study of half a million Swedish men adjusted for genetic confounding by comparing brothers and found no association between paternal age and offspring IQ.