# Results usually expressed in SD or SEM? - (Oct/07/2008 )

Hi,

SD or SEM? which one is more accurate and frequently used in statistic analysis?

If your points are a mean, use SEM.

That means I do 3 times, each time triplicates, so I have mean values for 3 times, then calculate the SEM for these three mean values?

I would recommend u going for the SD instead however.

I have read a lot of journal from the "big shot" ppl using SD. it's safer so to speak.

SD tells u the variability of ur sample.

however SEM tells how precise our estimate of the mean is relative to the population mean

for more information read

http://bja.oxfordjournals.org/cgi/content/full/90/4/514

"Background. In biomedical research papers, authors often use descriptive statistics to describe the study sample. The standard deviation (SD) describes the variability between individuals in a sample; the standard error of the mean (SEM) describes the uncertainty of how the sample mean represents the population mean. Authors often, inappropriately, report the SEM when describing the sample. As the SEM is always less than the SD, it misleads the reader into underestimating the variability between individuals within the study sample." - Nagele P ,2002.

My rule of thumb might be incorrect. Here is a rather impassioned argument for why you would want to use SD versus SEM, but it does come down to what it is you're trying to show the variability of...

Thanks Hanming86 for the paper