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Dr. Ruiz is studying how two different lighting conditions affect reading speed. Knowing that baseline reading speed varies widely between individuals, she decides to use a within-subjects design. Explain how Dr. Ruiz's design choice applies to controlling individual differences in reading speed, and describe the benefit this design has on her required sample size compared to a between-subjects design.
Question: Dr. Ruiz is studying how two different lighting conditions affect reading speed. Knowing that baseline reading speed varies widely between individuals, she decides to use a within-subjects design. Explain how Dr. Ruiz's design choice applies to controlling individual differences in reading speed, and describe the benefit this design has on her required sample size compared to a between-subjects design.
Sample answer: By testing the same individuals in both lighting conditions, Dr. Ruiz naturally controls for extraneous participant variables (like baseline reading speed). This reduces statistical noise, making it easier to detect any true effect of the lighting on reading speed, and means she will require fewer overall participants than a between-subjects design to detect an effect of the same size.
Key points:
- Testing the same individuals in all conditions naturally controls for extraneous participant variables.
- Reducing individual differences in this way decreases statistical noise in the data.
- The design requires fewer overall participants than a between-subjects design to detect an effect of the same size.
Rubric: Full credit should be awarded if the student explains that: 1) testing the same people in every condition controls for extraneous participant variables (baseline reading speed) and reduces statistical noise, and 2) this design requires fewer overall participants to detect the same size effect compared to a between-subjects design.
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Research Methods in Psychology - 4th American Edition @ KPU
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Dr. Ruiz is studying how two different lighting conditions affect reading speed. Knowing that baseline reading speed varies widely between individuals, she decides to use a within-subjects design. Explain how Dr. Ruiz's design choice applies to controlling individual differences in reading speed, and describe the benefit this design has on her required sample size compared to a between-subjects design.