So far, we have been talking about causes and effects in qualitative terms. An effect either occurs or does not occur; a factor is either present or absent. However, both sides of this equation can vary quantitatively as well. Concomitant variation（伴随） is the method in which a quantitative change in the effect is associated with quantitative changes in a given factor. Example:

If you car makes a funny noise when you accelerate, you might take your foot off the pedal and see whether the noise goes away. As we saw in the earlier example, that would be the method of difference. But you might also vary the pressure on the pedal to see whether the noise varies in intensity accordingly. That would be the method of concomitant variation.

若能收集到该词条相关资料的跟帖者给予奖励，根据收集资料的水平给予10～200不等的论坛币，当然也可以谈谈自己的观点、其应用领域、上传资料、相关软件介绍等等，请大家尽量不要复制一些搜索引擎很容易收集到的资料。

     我每天都会发送不等数量的词条，所以诚邀不同统计背景的各路大侠发表评论。

     欢迎大家多多跟帖！要数量也要质量哟