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

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 one of three domains: eating, friendships or 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 a response in the form of 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. What should the researcher conclude about his study, given these results?

Effect DFn DFd SSn       SSd        F     p

GROUP    2 27 6795.729 98210.579 0.934 .405

DOMAIN   2 54 67459.951 227046.533 8.022 .001 **

DOMAIN:GROUP 4 54 55061.976 227046.533 3.274 .018 *

Explanation / Answer

Please note that based on the results the p values(the last column in output table) are

group 0.405

domian 0.001

domain:group 0.018

assuming that are alpha value is 0.05 , we shall say that the effect is statisitcally significant if the p value is less than 0,05 , hence as shown in the output the only domain and domain: group are statistically significant,

Which means that the domain variable : eating freindship and physical world has a signifcant effect on the reaction time values.

At the same time , the interaction variable domian:group is also signficant , which means that there is an interaction between the domain variable and the group variable (control,anorexic, bulimic ) that has a significant effect on the reaction time values. However , to interpret the exact effect we must have the original data and then we shall plot the side by side boxplot to see the difference , or we can also plot a interactionplot in R to see how values of reaction time change based on group and domain variables.

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