Treatment effects, individual differences, and experimental error are the sources of variability for what?

Treatment effects, individual differences, and experimental error are the sources of variability for what?

• A. Between treatments
• B. Within treatments
• C. Experimental error
• D. Random sampling error

Answer: (A)

Focusing on how many and how large the differences are across treatment groups is key here. The variability that reflects differences between the treatment conditions—the extent to which the treatment group means differ from one another—is what the analysis of variance is designed to test. If these between-group differences are larger than what would be expected from random fluctuation, it suggests a treatment effect. Individual differences and experimental error contribute to what you see within each treatment group (the variation among individuals under the same treatment and measurement noise). They inflate the within-treatments variability, not the between-treatments variability. Random sampling error influences overall variability too, but the specific quantity that captures differences across treatments is the between-treatments variability.

Focusing on how many and how large the differences are across treatment groups is key here. The variability that reflects differences between the treatment conditions—the extent to which the treatment group means differ from one another—is what the analysis of variance is designed to test. If these between-group differences are larger than what would be expected from random fluctuation, it suggests a treatment effect.

Individual differences and experimental error contribute to what you see within each treatment group (the variation among individuals under the same treatment and measurement noise). They inflate the within-treatments variability, not the between-treatments variability. Random sampling error influences overall variability too, but the specific quantity that captures differences across treatments is the between-treatments variability.