Re: Interactions binary logistic regression

Posted by PhD student on Jan 23, 2017; 8:18pm
URL: http://spssx-discussion.165.s1.nabble.com/Interactions-binary-logistic-regression-tp5733602p5733737.html

1) As I do not have many trials per participants, although I have an “important” sample compared to others psychological studies with patients, my N = 648 (which is quite low I think).
All my significant effects (2/3 main effects; 1/3 two-way interactions; 1/1 three-way interaction) have a beta ranging from 1.3 (for the 3-way interaction) to 1.9, with an associated wald test ranging from 4 to 12.

2) In fact, although we can fear a basement effect due to the risk-aversion of individuals with Anxiety Disorders, overall means revealed that they chose the gamble option for 40% of trials vs. ~50% for control. When specifying all the conditions, the lowest value of gambling for the patients is 25%.
Looking at means, the three-way interaction is easily explained by the fact that both patients and controls are affected by the formulation in the low risk condition whereas only controls were still affected by the formulation in the high risk condition.

3) The main hypothesis of this study was that contrary to controls, individuals with AD would be susceptible to the formulation only in the high risk condition (which corresponds to the 3-way interaction).

However, we also had less specific hypothesis, such as both AD and controls would be affected, overall, by the formulation or AD would do overall less risky choices than controls but as my model included the 3-way interaction, I could not conclude on these hypotheses. Maybe an option could be to run 3 different models one including only main effect, one with main effects and two-way interactions and the third with the full factorial design, but I have never seen an example of this procedure for GEE.