Hi, I have a question about a regression I am running (actually an event history/survival analysis model, but my question should apply to all types of regression). In the original model, a variable--let's say the "geographic concentration of trees"--has a significant negative effect on the likelihood of the focal entity dying, given that it has survived so far. In the second model, I break up this variable into two exhaustive sub-variables: (1) the "geographic concentration of coniferous trees" and (2) the "geographic concentration of deciduous trees". Both these sub-variables have a negative coefficient but not a significant one.
My question is: Can a variable have a significant effect but its sub-variables not have significant effects (even though the signs of the coefficients are the same as the sign on the original variable)?