Final answer:
The method of random assignment is key for ensuring statistical validity in an experiment by reducing bias and ensuring each participant has the same chance of receiving each treatment.
Step-by-step explanation:
To determine which of the following provides information about the statistical validity of Dr. Lonsbary's study, we must consider the principles of experimental design and statistical analysis. Statistical validity refers to how well the results of a study support the conclusions that are drawn from it. Specifically, in this context:
- The mood reported by the participants is not directly related to statistical validity.
- The method of random assignment is a crucial component of experimental design that can contribute to statistical validity by ensuring that each participant has an equal chance of receiving each treatment, thereby reducing bias.
- The d coefficient (often used to measure effect size) provides information about the magnitude of a treatment's effect, which can be relevant for evaluating the practical significance of study results, but alone does not establish validity.
- The number of people in each group can affect the power of the study but is not a direct measure of validity. However, too small a sample size can lead to lack of statistical power to detect a true effect.
Therefore, the correct answer is b. The method of random assignment provides information about the statistical validity of Dr. Lonsbary's study.