Researchers were interested in comparing the long-term psychological effects of being on a high-carbohydrate, low-fat (LF) diet versus a high-fat, low-carbohydrate (LC) diet. A total of 106 overweight and obese participants were randomly assigned to one of these two energy-restricted diets. At 52 weeks, 32 LC dieters and 33 LF dieters remained. Mood was assessed using a total mood disturbance score (TMDS), where a lower score is associated with a less negative mood. A summary of these results follows. Group n x-bar s

LC 32 47.3 28.3

LF 33 19.3 25.8

(a) Is there a difference in the TMDS at week 52? Test the null hypothesis that the dieters'

average mood in the two groups is the same. Use a significance level of 0.05.

(b) Critics of this study focus on the specific LC diet (i. e., the science) and the dropout rate.

Explain why the dropout rate is important to consider when drawing conclusions from this

study.