Hi , In nominal logistic fit. I get a significant model, all parameters are significant by the effect LRT. but all the parameters estimations are not significant. how can it be??
The cause is collinearity among the independent variables.
The overall test just says that the model including all the variables is better than the mean of the response.
The test for significance of the individual parameters is conditioned on all the other parameters in the model.
If there is substantial correlation between two independent variables, both important in explaining the response, then neither will be significant with the other in the model.
Collinearity can be more complicated than just two variables being correlated. It can happened if one variable is correlated with a linear combination of several other variables which is common when one has many independent variables.
The solution in general is to identify the subsets of variables that are highly correlated among each other and use a subset that is not too correlated.
Not being a JMP expert, more SAS, I will leave it to others to give you more specific advice on how do identify the highly correlated subsets
Some ideas that come to mind are looking at pairwise correlations. Another idea is to use the partition platform to pick candidate independent variables.
If your goal is prediction, then using recursive partitioning is fine. If you goal is inference, using recursive partitioning to select variables will bias the p-values small and make any inference suspect.
Are your parameter estimates labeled "unstable"? If so, you might want to take a look at this JMP note:36686 - When I run nominal or ordinal logistic regression in JMP®, I receive parameter estimates lab...
Another potential approach if multicollinearity among your predictor variables is an issue is, if you are running JMP Pro, the Generalized Regression Lasso/Elastic Net personalities are viable modeling options as well.