lead individuals to conclude there is a fan-shaped interaction because they are essentially failing to measure, with reference to Figure 1b, environments –2 and –1, which represent the positive end of the environmental continuum. In looking at Figures 1a and b, one can imagine a number of other incorrect conclusions that could be drawn about the nature of gene-environment interaction effects as a result of restricted range of environmental measures. For example, in Figure 1b, measurement of individuals from environments –2 to 0 would lead one to conclude that genetic effects play a stronger role at lower levels of environmental exposure. Measurement of individuals from environments 0 to 2 would lead one to conclude that genetic effects play a stronger role at higher levels of exposure to the same environmental variable. In Figure 1a, if measurement of individuals was limited to environments –2 and –1, depending on sample size, there may be inadequate power to detect deviation from a purely additive genetic model, e.g., the slope of the genotypic lines may not be significantly different.
