There are other possible reasons for being unable to predict phenotypes with greater precision. First, different cognitive phenotypes were used in each cohort. However, this should not be over-emphasised as it has been shown clearly that the general factors derived from different mental test batteries tend to rank people almost identically5. In the case of crystallized intelligence—where single tests were used—different vocabulary tests are very highly correlated. Second, there may be genetic differences between the UK and Norwegian populations which could result in dissimilar patterns of LD38 (Supplementary Figure 1). However, this is unlikely to be important because LD is very similar across European populations38.
