During study our of statistics in my psychology coursework, we had to teach ourselves how to use generalized linear models in SPSS (only basic knowledge). For an exam we may also use generalized linear models and I want to try it, but I have two problems:
According to the distribution of the dependent variable, a normal distribution would fit our data best. A fellow student said that this is not logical, because our dependent variable is "time required to complete a task", so it cannot have negative values. Our lecturer wrote on his slides that a variable needs to be able to range from $-∞$ to $+∞$ to use the normal distribution.
In another post in these sides, I read that the normal distribution creates a predicted variable which fits these characteristics, so the original dependent variable doesn't need to fulfill those characteristics. Is that true?
As I can't use the normal distribution, a Gamma distribution would fit best. According to SPSS's documentation, the canonical link function is Power(-1). I don't quite understand what I have to put in the box "Power" in SPSS. Do I have to fill in 0,05 if I want to work with a Power of 0,95 (so Power(-1) would mean 1-0,95) or do I have to fill in -1 as value of power (which seems quite unusual to me).