A second approach is to design a better test, i.e. one in which item difficulties span a wide range of latent trait values, resembling the second simulated test in the examples above. In this case, regression analysis of a 20-item test recovers the “true” (additive) model with parameter sampling errors close to those that would be obtained if the true trait values were measured and little evidence for genetic effects on linear response to the environment. However, even a better test of this type is still affected by issues of scale.
