What you read is correct. If the interaction is significant, interpreting either main effect, whether significant or not, is basically pointless (and misleading). The reason is that when A and B are involved in an interaction, the coefficient for A is the effect of A when B=0; in other words, the effect is conditional on the value of B, and is not a main effect. Similarly, the coefficient for B is the effect of B when A=0.
The fact that A is significant merely means that A has an effect when B=0. Similarly, the fact that B is not significant merely means that B doesn't have an effect when A=0, though it probably does have an effect for other values of A; this is precisely why the interaction is significant.
What you would need to do is look at simple slopes, which shows the significance of the A effect as a function of the B variable. You need to determine at which values of B does A have an effect, and vice-versa. Kris Preacher provides an online tool to decompose 2-way interactions in linear mixed models.
What you read is correct. If the interaction is significant, interpreting either main effect, whether significant or not, is basically pointless (and misleading). The reason is that when A and B are involved in an interaction, the coefficient for A is the effect of A when B=0; in other words, the effect is conditional on the value of B, and is not a main effect. Similarly, the coefficient for B is the effect of B when A=0.The fact that A is significant merely means that A has an effect when B=0. Similarly, the fact that B is not significant merely means that B doesn't have an effect when A=0, though it probably does have an effect for other values of A; this is precisely why the interaction is significant.What you would need to do is look at simple slopes, which shows the significance of the A effect as a function of the B variable. You need to determine at which values of B does A have an effect, and vice-versa. Kris Preacher provides an online tool to decompose 2-way interactions in linear mixed models.
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