Why Does Generalizing a Multiple Regression Equation to Another Sample

Multiple Choice

Why does generalizing a multiple regression equation to another sample tend to produce a lower R² in the second sample?

A) the internal validity of nonexperimental methods is lower than for experimental methods
B) the external validity of nonexperimental methods is lower than for experimental methods
C) the regression equation assumes that data are free from measurement error, so any error present in sample 1 will likely be different from error in sample 2, and in turn, decreasing the amount of correspondence between sample 1 regression weights and sample 2 data.
D) the regression equation assumes that data are free from sampling error, so any error present in sample 1 will make the regression weights artificially high, and in turn, sample 2 reveals variable weights that are more accurate reflections of reality