There were a number of errors in Fig. 1 in the paper by Mitchell et al. (Reference Mitchell2010) for which the authors apologize.
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Fig. 1. Only four items per twin are shown. Λ1.1 denotes the factor loading for the first item, for twin 1. A1.1 denotes the residual variance due to A for the first item, for twin 1. r a.1=1.0 or 0.5 and denotes the twin correlation for the residual components due to A for the first item, etc. r c.1=1.0 and denotes the twin correlation for the residual components due to C for the first item, etc.
The correct version of Fig. 1 is given on the following page.