standard error of measurement
The standard deviation (SD) represents variation in the values of a variable, whereas the standard error of the mean (SEM) represents the spread that the mean of a sample of the values would have if you kept taking samples. So the SEM gives you an idea of the accuracy of the mean, and the SD gives you an idea of the variability of single observations. The two are related: SEM = SD/(square root of sample size).
简单地说就是平均数的抽样误差,反映平均数的抽样准确性,国内用标准偏移值SD的较多,SEM=SD除以(样本数的平方根)……
SEM:搜索引擎营销,现在的SEM环境比较差,效果逐年降低,主要是受到SNS方面的影响还有很多APP也分流了,导致搜索客户下降SEM团队的建设主要根据你现有的项目需求搭建,还要只当配备美工,要有前端和后台的支持,针对活动或者专题来做
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