I need help clarify something. I had about 300 youths to investigate the association between perceptions and treatment adherence. I categorized age into three: children, young adolescents, and older adolescents. When I enter the data in SPSS and did multinomial logistic regression (three outcomes), there was no interaction detected, but when I stratified them by three age groups, the effect size as well as significance was very different among three groups. I just wonder why I could not detect the interaction. Is it possible that I did not have enough sample for the detection? Or am I talking about different things? Thank you for your help.