Mean ± SEM or Mean(SD)

1.
The common descriptive statistics is mean and standard deviation (SD)
SD 平均值和标准偏差

Data not following the normal distribution, it is median and range
适用的数据不遵循正态分布，是个中位数和范围

The SD quantifies scatter : how much the values vary from one another

The SD does not change predictably as you acquire more data.The SD quantifies the scatter of the data, and increasing the size of the sample does not increase the scatter.
相反，SD不会随着样本数量的增加而变化
SD表明了数据的分散程度 样本量的增加不一定会增加分散程度

The SD will stay the same as sample size gets larger.
样本增大可能SD值也会保持不变

If the scatter is caused by biological variability, your probably will want to show the variation. In this case, graph the SD rather than the SEM.
如果生物变异引起了分散，如果想要表现这种变异，就要使用SD而不是SEM

you could also instruct Prism to graph the range, with error bars extending from the smallest to largest value. Also consider graphing every value, rather than using error bars.

可以用Prism软件绘制范围， 误差bars 从最小值到最大值
还要考虑到画出每个值，而不是仅仅使用error bars.

If you are using an in vitro system with no biological variability , the scatter can only result form experimental imprecision. In this case, you may not want to show the scatter, but instead show how well you have assessed the mean. Graph the mean and SEM or the mean with 95% confidence intervals.
如果是体外实验，也就是没有生物学变异，那么数值的分散程度就是由于实验偏差引起的。这种情况下，你要表现的不是分散程度，而是对平均值的估计。
画的是平均值和SEM (95%的置信区间)

Ideally, the choice of which error bar to show depends on the source of the variability and the point of the experiment. In fact, many scientists always show the mean and SEM, to make the error bars as small as possible.

使用哪种error bar 取决于变异程度和实验点
事实上，研究人员常常画的是 SEM 使得error bars 尽可能小

2.
mean and standard error of mean (SEM)
平均值和平均值标准误差

used to describe the variability within the sample
描述变量间的差异

The SEM quantifies how accurately you know the true mean of the population.
SEM 计算这个群体的平均值有多精确

The SEM gets smaller as your samples get larger. This make sense, because the mean of a large sample is likely to be closer to the true population mean than is the mean of a small sample.
样本越大SEM值越小，应为大样本的平均值可能更接近真实的平均值

The SEM is a measure of precision for an estimated population mean
is not a descriptive statistics and should not be used as such
SEM 是预计群体平均值的精确程度的测量手段，不是描述性的数据

many authors incorrectly use the SEM as a descriptive statistics to summarize the variability in their data because it is less than the SD, implying incorrectly that their measurements are more precise

The SEM is correctly used only to indicate the precision of estimated mean of population.Even then however, a 95% confidence interval should be preferred.
SEM正确的用法是表示群体的预计平均值是否精确。95%的置信区间。

Further, while reporting mean and SD, instead of writing “mean ± SD” the better way of representation would be “mean (SD)” as it will decrease the chance of confusion which confidence interval
使用的时候不要写成 mean ± SD, 最好写成 mean(SD)