What can we conclude about the main effect of the group variable?

Question

An experiment was conducted to see how people with eating disorders differ in their

need to exert control in different domains. Participants were classified as not having an

eating disorder (control), as having anorexia nervosa (anorexic), or as having bulimia

nervosa (bulimia). Each participant underwent an experiment that indicated how much

they felt the need to exert control in three domains: eating, friendships and the physical

world (this final category was a control domain in which the need to have control over

things like gravity or the weather was assessed). So all participants gave three

responses in the form of a mean reaction time; a low reaction time meant that the

person did feel the need to exert control in that domain. The variables have been

labelled as group (control, anorexic, or bulimic) and domain (food, friends or physics).

The R output from an analysis is shown below and the next two questions relate to this

output.







a. People with eating disorders need to exert more control over different

domains of their life, F(2, 27) = 0.93, p < .05.

b. When ignoring the type of domain, people who differ with regard to eating

disorders did not significantly differ in their need to exert control, F(2, 27) =

0.93, p > .05.

c. People with eating disorders significantly differ in their need to exert control

over food, F(2, 27) = 0.93, p > .05

d. People with eating disorders need to exert significantly more control over

different domains of their life than people without eating disorders, F(1, 27) =

2029.76, p < .001.

Answer 1

b. When ignoring the type of domain, people who differ with regard to eating
disorders did not significantly differ in their need to exert control, F(2, 27) =
0.93, p > .05.