Question

A psychopharmacologist conducted a study on the effects of the drug lithium for the treatment of depression. Twenty-seven patients were chosen whose principal problem was depression. There were 3 groups: Placebo, Low Dose (50mg) and High Dose (200mg). There were 9 patients in each group. At the end of 30 days, the patients were evaluated for their level of depression, with higher scores indicating higher levels of depression.

                Fill in the blanks with the appropriate numbers, setting alpha=.05.

Source                  SS           df            MS         F              p

Total                      _____   __

Between             143.41   __           ___        ___        ___

Within                   365.11   __           ___

Which of the following is true of between-subjects ANOVA?

   A)           Participants provide data for just one condition/level of the independent variable.

                B)            Participants contribute data to every condition/level of the independent variable.

3.            A between-subject ANOVA is similar to an independent t-test, EXCEPT _____.

   A)           that in a between-subjects ANOVA , the IV cannot have more than two levels

                B)            that in a between-subjects ANOVA, the DV cannot exceed the alpha level

                C)            that in a between-subjects ANOVA, the IV can have three or more levels

                D)           that in a t test, the DV has to be nominal

In a J=3 between-subjects ANOVA, we find that the p-value is 0.003. We therefore conclude that:

   A)           there is no statistical evidence that any group mean is different from any other

                B)            all group means are equal

                C)            all group variances are equal

                D) all group means are different

                E)            the null hypothesis should be rejected

Answer 1

Source                  SS           df            MS         F              p

Total                      508.52   26

Between             143.41   2           71.705        4.713428        0.01876673

Within                   365.11   24 15.21292

SS for Total = SS for Between + SS for Within

= 143.41 + 365.11 = 508.52

df for Total = n - 1 = 27 - 1 = 26

df for Between = Number of groups - 1 = 3 - 1 = 2

df for Within = n - Number of groups = 27 - 3 = 24

MS for between = SS for Between / df for Between

= 143.41 / 2 = 71.705

MS for Within = SS for Within / df for Within

= 365.11 / 24 = 15.21292

F = MS for between / MS for Within

= 71.705 / 15.21292

= 4.713428

P-value = P(F > 4.713428, df = 2, 24) = 0.01876673

For between-subjects ANOVA,

                B)            Participants contribute data to every condition/level of the independent variable

3.            A between-subject ANOVA is similar to an independent t-test, EXCEPT _____.

                C)            that in a between-subjects ANOVA, the IV can have three or more levels

In a J=3 between-subjects ANOVA, we find that the p-value is 0.003. We therefore conclude that:

                E)            the null hypothesis should be rejected