Suppose we have the following regression, with Sun=0 for partial sun and Sun=1 for full sun:
Plant Height = a0 + a1*Bacteria + a2*Sun + a3*Bacteria*Sun
And here is the sample output from R:
According to this post, for plants with full sun (Sun=1), the effects of Bacteria is: -0.08346 + 0.03368 = -0.04978, meaning that for two plants with full sun, the plant with one unit more bacteria will be 0.04978cm shorter.
So my question is, is this difference significant?
Since we get the above conclusion by combining the coefficients of Bacteria and Bacteria*Sun, but as in the output, the first coefficient has a significant p-value=0.00214 while the other coefficient for the interaction term has a large p-value=0.34887.
So when we add these coefficients, how should we interpret its significance?