I am a first year psychology student. I am doing some research work with a prof, unfortunately the material that I need to use right now is covered only in my second year. But I need to already know it now. So I am burning through any resources I can find to quickly come up to speed. I need help to understand this particular situation here. Involves SAS, Regression Analysis.
When I ran a regression in SAS ( proc reg ) using two variables say a and b. I got this. I understand this as saying that both these variables (a&b) do not significantly predict my target variable. Here is the SAS output.
Analysis of Variance Sum of Mean Source DF Squares Square F Value Pr > F Model 2 3.32392 1.66196 1.00 0.3774 Error 46 76.80649 1.66971 Corrected Total 48 80.13041 Root MSE 1.29217 R-Square 0.0415 Dependent Mean -0.23698 Adj R-Sq -0.0002 Coeff Var -545.26074 Parameter Estimates Parameter Standard Standardized Variable DF Estimate Error t Value Pr > |t| Estimate Intercept 1 -0.25713 0.18515 -1.39 0.1716 0 a 1 -0.35394 0.28797 -1.23 0.2253 -0.19510 b 1 -0.04706 0.39586 -0.12 0.9059 -0.01887
Now I tried to include the interaction of a and b into the picture. Lets call it aXb, now the out put indicates that a and aXb significantly predict my target variable.
Analysis of Variance Sum of Mean Source DF Squares Square F Value Pr > F Model 3 16.64439 5.54813 3.93 0.0142 Error 45 63.48602 1.41080 Corrected Total 48 80.13041 Root MSE 1.18777 R-Square 0.2077 Dependent Mean -0.23698 Adj R-Sq 0.1549 Coeff Var -501.20683 Parameter Estimates Parameter Standard Standardized Variable DF Estimate Error t Value Pr > |t| Estimate Intercept 1 -0.06807 0.18098 -0.38 0.7086 0 a 1 3.01517 1.12795 2.67 0.0104 1.66201 b 1 -0.00994 0.36407 -0.03 0.9783 -0.00399 aXb 1 -1.13782 0.37029 -3.07 0.0036 -1.90743
Here are my questions: I am not sure what to make out of this situation. Taken together what does this indicate to me? Also while you are answering the question, could you supplement it with some resources, goog keywords etc for me to learn more surrounding these topics.
Thank you so much for your help.