Logic of Causal Inference in Controlled Experiments
The fundamental principle of a controlled experiment is to ensure that the only significant difference between the experimental and control groups is the experimental manipulation itself. By isolating this single variable, any subsequent, statistically meaningful differences observed in the dependent variable between the groups can be confidently attributed to the manipulation. This rigorous design allows researchers to infer a cause-and-effect relationship.
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Ch.2 Psychological Research - Psychology @ OpenStax
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Control Group
Experimental Group
Example of a Two-Group Experiment: Technology in the Classroom
Logic of Causal Inference in Controlled Experiments
A researcher is conducting an experiment to determine if a new energy drink improves participants' performance on a complex puzzle. One group of participants drinks the new energy drink, while a second group drinks a similar-tasting beverage without the active ingredients. Both groups are then timed on how long it takes them to solve the same puzzle. For the researcher to validly conclude that the energy drink caused the observed difference in puzzle-solving times, which of the following is the most critical condition of the research design?
Factorial Design
Logic of Causal Inference in Controlled Experiments
A researcher wants to test the effectiveness of a new public speaking training program. They allow the first 40 volunteers who sign up to participate in the new program (the experimental group). The next 40 volunteers are assigned to a waitlist and will serve as the control group. The researcher finds that the experimental group performs significantly better on a final speaking task. Why is it difficult to conclude that the training program caused the improvement?
Problem of Systematic Differences in Experiments
What is the primary purpose of using random assignment in an experimental design?
In an experiment with 200 participants, a researcher uses random assignment to place participants into either a meditation group or a control group. A colleague argues that random assignment guarantees the two groups will have identical average ages, stress levels, and personality traits before the study begins. Is this claim accurate?
Cause-and-Effect Relationship
Example of a Causal Claim in Experimental Research
Random Selection in Experiments
Random Assignment in Experiments
Logic of Causal Inference in Controlled Experiments
A researcher reviews the findings from four different studies. Which of the following conclusions could only have been drawn from a study using an experimental design?
Blinding in Experiments
Conditions for Causal Statements in Experiments