N in Cell Culture - What is the proper way to determine your "n"? (Apr/23/2008 )
So I am having a "discussion" with a fellow lab member about the proper way to determine the n for your experiment. Often you see in papers that the n=6 from two seperate experiments, and I interpret that as two seperate experiments tripilicate. My current mentor says that should be an n=two, while clearly it is acceptable in journals, but is it correct?
Does it depend on how the duplicates are seeded (ie different plates on the same day versus multiple wells on the same plate)?
Does it depend on the cells used (all from the same stock versus from different stocks or different donors)?
Is there anywhere I can find real guidelines to these issues?
Thanks in advance, I look forward to a lively discussion with a lot of different view points.
you can find some answers to your questions in the paper by Cumming et al., "Error Bars in experimental Biology" Journal of Cell Biology (2007), Vol 177, 7-11
i'm copying a part of the text regarding the use of cell cultures below:
"Similarly, a number of replicate cell cultures can be made by pipetting the same volume of cells from the same stock culture into adjacent wells of a tissue culture plate, and subsequently treating them identically. Although it would be possible to assay the plate and determine the means and errors of the replicate wells, the errors would reflect the accuracy of pipetting, not the reproduciblity of the differences between the experimental cells and the control cells. For replicates, n = 1, and it is therefore inappropriate to show error bars or statistics."
I think some people will agree with this, while others will disagree. As you often see things like this published, I think it's up to the authors' opinion (but reviewers might have another opinion of course )
Thanks for the reference. Very informative.