I am having difficulties in understanding the difference between interaction terms and test for interaction. I am using logistic regression models so maybe the concept is different compared to linear regression?
As far as I understood from this explanation, interaction terms let you know how the relationship between two variables changes when a third variables assumes different values. For example: how relationship between death and age changes according to sex (e.g. if sex=male or sex=female how the OR changes). But from the interaction terms I can also know if there is a significant difference between the changes due to sex, is this correct? This is the source from what I understood this.
So what is then the point of performing tests for interactio)? For instance, I run a logistic regression in males to obtain the OR for death and age and then I run the logistic regression for females to obtain the OR, and then I compare the two ORs using test for interaction.
What is the correct method to assume that two subgroups (e.g. males and females) have a significantly difference relationship between age and death? What are the differences between interaction terms and test for interaction?