Which experimental design means that two groups of test units were randomly assigned to two different treatment groups at the same time, and the dependent variable was measured in the two groups simultaneously? A)R X₁ O₁ R X₂ O₂ B)R X₁ O₁ O₂ X₂ O₃ C)X O₁ O₂ X O₁ O₂ D)R X₁ O₁ R X₁ O₁

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This experimental design is called a parallel design or two-group posttest-only design. It involves random assignment of test units to two treatment groups (R), followed by the application of the treatment (X1 or X2), and then the measurement of the dependent variable (O1 or O2). The two groups are measured simultaneously, which reduces the potential confounding effects of time or history. This design allows for a comparison of the mean differences between the treatment groups and provides a more rigorous test of the treatment effect.

Which Experimental Design Means That Two Groups of Test Units