When some main fac tors change, there is uncertainty in economic forecast if the forecast method is used as usual.
经济预测中发生主要影响因素改变时，若采用通常的预测方法会因历史数据过少而出现较大误差。
2
Objective to identify the cause and transmission route of hepatitis a, to analyse the epidemic fac - tors and to evaluate the control effect.
目的查明甲肝暴发原因和传播途径，分析流行因素，评价控制效果。
3
Objective to understand the current status of sports behavior of workers in Shenzhen City from outside and the fac-tors affecting their regular sports.