In a forward stepwise logistic regression – I appear to have a -2 Log Likelihood of 145.104, but I thought probabilities were always less than 1?
Indeed they are. But what you are looking at is not a probability but the NEGATIVE LOG of a likelihood RATIO. i.e. we have found 2 probabilities – both lying, to be sure, between 0 and 1. But then we have taken the ratio of them – which could give us any positive number whatsoever. Then we’ve taken the log of that, which means from a positive number we can get anything from minus infinity to plus infinity. Finally we’ve negatived that. Since -2LLR comes out positive, LLR must have been negative; so the LR was less than one (remember that log 1 is zero, log x is positive for x>1 and negative for x<1) Q: O.K. I can understand that if -2LLR is positive, LLR is negative. What I fail to understand is how that '-2 Log likelihood' that SPSS gives up relates to the LRFC statistic ie. how it helps us to see how well we can classify people into groups from a knowledge of the independent variables (point 1 of 'a reassuring coda'). A: The "Model Chi-Square" that SPSS gives you is twice the differe
