Sample Size Sample average Sample SD Diagnosed early bird 67 1.23 0.93
Diagnosed night owl 59 2.10 0.99

Analyze the data using a theory-based approach (use the Theory-based Inference applet) to determine whether early birds differ from night owls with respect to average nightmare frequency. The data are not strongly skewed within each group.

Express the null and alternative hypotheses for testing.

a. Null: The population average VDAS score for early birds is less than the population average VDAS score for night owls.
Alt: The population average VDAS score for early birds is greater than the population average VDAS score for night owls.

b. Null: The population average VDAS score for early birds is the same as the population average VDAS score for night owls.
Alt: The population average VDAS scores are different for the two groups.

c. Null: The population average VDAS scores are different for the two groups.
Alt: The population average VDAS score for early birds is the same as the population average VDAS score for night owls.

d. Null: The population average VDAS score for early birds is greater than the population average VDAS score for night owls.
Alt: The population average VDAS score for early birds is less than the population average VDAS score for night owls.