自己搞明白了,如果有大虾有不同意见,请指正。我主要参考
http://support.sas.com/kb/24/447.html#ex4
Constructing a Likelihood Ratio Test
Note that the two models above are considered nested because the main-effects model is just the saturated model with several parameters (the interaction parameters) set to zero. You can compare two nested models by computing a likelihood ratio (LR) test statistic, which is twice the ratio of the models' likelihood values, or equivalently and more conveniently, twice the difference in their log likelihood values. For these models, twice the difference in their log likelihoods is 8.228. The LR statistic is chi-square distributed with degrees of freedom (DF) equal to the number of parameters being tested—seven in this case, because there are seven DF that are associated with the four interactions. To get a p-value for the LR statistic, use the PROBCHI function in the DATA step. The following statements produce a p-value for the LR test comparing the main-effects and saturated models:
data lrt;
lr=2*(-682.2478 - -686.3618);
df=7;
p=1-probchi(lr,df);
run;
proc print noobs;
format p pvalue.;
run;
The null hypothesis being tested is that the saturated and main-effects models are equivalent. For this to be true in this example, the interaction parameters must all be zero. So, the null hypothesis can be stated generally as model equivalency, or in this example it can be stated as lack of interaction. The results show that the null hypothesis cannot be rejected (p=.3129).