SPSS output

I faced a problem in explaining the SPSS Analysis of Variance output. What is the difference between “main effect” and “interaction effect”?

1 comment to SPSS output

  • Roy

    In SPSS research, both main effect and interaction effect are very important for interpretation. According to the definition, “Main effects are differences in means over levels of one factor collapsed over levels of the other factor”. If you have two levels, then the main effect can show such outcome where the outcome has consistent difference between the levels of any specific factor.

    Do you feel hard to understand? I can put an example here. If you want to know the effectiveness of watching TV between two groups where one group watches TV for 14 hours in a week and another group does the same only for 2 hour per week considering a specific factor, you can use main factors.

    On the other hand, according to the definition, “Interaction effect is a change in the simple mean effect of one variable over levels of the second”. In interaction effect, a number of set parameters are used to explain the differences between the levels. However, all the parameters can show a significant interpretation only when these are used or analyzed collectively, not separately.

    To work with main effect, you can consider the factorial designs which are very useful to understand the interpretations of data properly. Besides, you can find different situations or factors working with both main effect and interaction effect and you always should be careful about those situations or factors. If you work with three separate effects of a variable, then there are total eight combinations exist. Two, three or four may or may not be significant from the eight possible combinations of effect. And for interaction effect, you should remember that interaction is happened between factors, not levels. If you work with time spent in office and office treatment, you can easily find interaction between those. But for that you will have to consider the office time and office settings, not the only hours or settings, and then you will have to describe the specific levels.

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