医学统计学方向，想做知识态度和行为与疫苗接种情况的结构方程模型，但是用Amos做出来模型识别不了，在结果中说“the model is probably unidentified. in order to achieve identifiability, it will probably be necessary to impose 1 additional constraint”也就是说要增加一个限制，但是要怎能解决啊？在线等！急！