study investigated if psychotherapy combined with limited administration of 3,4 Methylenedioxymethamphetamine (MDMA) can reduce symptoms of post-traumatic stress disorder. Severity of symptoms was measured via the CAPS-IV score with higher scores indicating more severe symptoms. Subjects recruited to the study were randomly allocated to one of the three dosage levels of MDMA (Low - 40 mg, Medium - 100 mg, High - 125 mg). The primary outcome was the reduction in CAPS-IV score at one month after the second treatment session. A secondary outcome was whether the subject experienced a drop of 20% or more in CAPS-IV score.

BeforeCAPS-IV score before treatment

AfterCAPS-IV scores at the one month after the second treatment session

ChangeReduction in CAPS-IV scores (Before - After)

DropWas a 20% reduction in CAPS-IV score achieved (TRUE or FALSE)

DoseDosage of MDMA given (Low - 40 mg, Medium - 100 mg, High - 125 mg)

Based on the information above, which of the following best describes the study?

Randomised complete block design

Randomised comparative double-blind experiment

Randomised comparative experiment

Observational study

Question 2

The mean CAPS-IV score before treatment in the low dosage group is

63.1

77.0

77.6

78.2

Question 3

Researchers conduct a one-way ANOVA to determine if there is a difference in the mean reduction in CAPS-IV for the three dosage levels of MDMA. Which of the following describes the null hypothesis that is tested in a one-way ANOVA?

The mean change in CAPS-IV score is zero for all dosage levels

The mean change in CAPS-IV score is the same for all dosage levels

The mean change in CAPS-IV score is different for at least one dosage level

The mean change in CAPS-IV score is different for all dosage levels

Question 4

What is the residual degrees of freedom in the one-way ANOVA to compare the mean reduction in CAPS-IV between the three dosage levels of MDMA?

2

47

51

53

Question 5

What is the Total Sum of Squares for this one-way ANOVA?

38.9

221.2

260.1

390.1

Question 6

Based on the F test for this one-way ANOVA, you can conclude there is

no evidence to suggest that there is an effect of MDMA dosage on the mean change in patient's CAPIS-IV score (p > 0.1)

weak evidence to suggest that there is an effect of MDMA dosage on the mean change in patient's CAPIS-IV score (p < 0.1)

moderate evidence to suggest that there is an effect of MDMA dosage on the mean change in patient's CAPIS-IV score (p < 0.05)

strong evidence to suggest that there is an effect of MDMA dosage on the mean change in patient's CAPIS-IV score (p < 0.01)

Question 7

What is the R2 value for this one-way ANOVA?

0.1497

0.2855

0.3869

0.8503

Question 8

Which of the following is NOT an assumption of this one-way ANOVA?

There is a linear relationship between mean change in CAPS-IV score and dosage

The changes in CAPS-IV score are independent

The change in CAPS-IV score has a normal distribution

The variability of the change in CAPS-IV scores does not depend on the dosage

Question 9

Which of the following would be most useful in assessing model assumptions?

Scatterplot of the fitted values from the one-way ANOVA against dosage

Normal probability plot of the changes in CAPS-IV score

Scatterplot of Before against After CAPS-IV scores

Normal probability plot of the residuals from the one-way ANOVA

Question 10

The researchers would like to understand which (if any) dosages of MDMA result in different mean changes in CAPS-IV score. Using Tukey's Honestly Significant Difference, the researchers are able to conclude that the mean changes in CAPS-IV score are different at the 5% (familywise) significance level for the following pairs of dosages:

Only Low-High

Medium-Low and Low-High

Medium-High and Low-High

Medium-Low, Medium-High and Low-High

Question 11

A secondary outcome for the experiment was whether subjects experienced a 20% drop in CAPS-IV scores at one month after the second treatment session. How many subjects in the study experienced a 20% drop in their CAPS-IV score?

4

8

23

24

Question 12

What proportion of participants received a low dosage of MDMA and experienced a 20% drop in their CAPS-IV score?

0.093

0.217

0.241

0.278

Question 13

If there was no association between experiencing a 20% drop in CAPS-IV score and dosage level, what is the expected count for subjects in the low dosage group experiencing a 20% drop in CAPS-IV score?

7.67

9.00

11.74

15.00

Question 14

What is the value of the 2 statistic used to test for an association between experiencing a 20% drop in CAPS-IV score and dosage level?

2.424

2.918

3.204

4.031

Question 15

What is the degrees of freedom for the 2 test in Question 14?

2

3

5

6

Question 16

Based on this analysis, you can conclude that there is

no evidence to suggest that there is an association between dosage level and experiencing a 20% drop in CAPS-IV score (p = 0.149)

no evidence to suggest that there is an association between dosage level and experiencing a 20% drop in CAPS-IV score (p = 0.295)

no evidence to suggest that there is an association between dosage level and experiencing a 20% drop in CAPS-IV score (p = 0.298)

no evidence to suggest that there is an association between dosage level and experiencing a 20% drop in CAPS-IV score (p = 0.702)

Before	After	Change	Drop	Dose
80	64	16	FALSE	Medium
79	60	19	TRUE	Medium
79	63	16	TRUE	Medium
80	63	17	TRUE	Medium
77	61	16	TRUE	Medium
74	59	15	TRUE	Medium
77	62	15	FALSE	Medium
80	65	15	FALSE	Medium
79	67	12	FALSE	Medium
79	63	16	TRUE	Medium
77	62	15	FALSE	Medium
81	68	13	FALSE	Medium
74	60	14	FALSE	Medium
78	62	16	TRUE	Medium
81	63	18	TRUE	Medium
81	64	17	TRUE	Medium
81	66	15	FALSE	Medium
78	63	15	FALSE	Medium
77	60	17	TRUE	Low
78	63	15	FALSE	Low
75	58	17	TRUE	Low
77	63	14	FALSE	Low
74	59	15	TRUE	Low
80	64	16	FALSE	Low
80	63	17	TRUE	Low
76	59	17	TRUE	Low
77	65	12	FALSE	Low
82	68	14	FALSE	Low
77	63	14	FALSE	Low
77	66	11	FALSE	Low
78	66	12	FALSE	Low
76	63	13	FALSE	Low
77	69	8	FALSE	Low
79	67	12	FALSE	Low
78	65	13	FALSE	Low
79	65	14	FALSE	Low
78	60	18	TRUE	High
80	63	17	TRUE	High
76	58	18	TRUE	High
78	64	14	FALSE	High
77	62	15	FALSE	High
80	64	16	FALSE	High
78	63	15	FALSE	High
79	68	11	FALSE	High
76	60	16	TRUE	High
79	62	17	TRUE	High
77	58	19	TRUE	High
80	65	15	FALSE	High
78	60	18	TRUE	High
76	61	15	FALSE	High
78	65	13	FALSE	High
81	64	17	TRUE	High
76	58	18	TRUE	High
83	69	14	FALSE	High