Im analyzing the impact of different biomarkers and clinical risk scores on postoperative complications and Id like to test the importance that every factor has on the final outcome. Even if I add the same Variables, Factors and Covariates in Neural Networks (Multilayer Perceptron Network) in SPSS, I get the different result every time. What could the problem be? And what is the minimum sample size for the proper analysis in NN since it needs samples for both training and testing?