Questions on how to present data on graph - (May/06/2007 )

Hi, I have previously read in this forum something on data presentation. I couldn't trace the original thread but it reads like this (sorry to the original contributor because I might have editted some words):

Triplicate is one experiment. You analyze in triplicate to be sure that there was no measurement error. Then you can do the mean of your triplicate but you don't show the standard deviation.
Then, you have to show that your results are reproducible, that your cells will behave the same way an other day. (today there was maybe some contaminants in the air, that gave you this result, and not tomorrow , or maybe you made a mistake in the treatment, which will be the same for all the triplicates, but you won't make again this mistake tomorrow...).
Then you can make a mean of your three experiments, and show the standard deviation, and make statistical analysis on your three experiments (9 reps)[/indent]

If I am going to plot a graph, may I know whether I need to get the mean from the 3 separate experiments and show the standard deviation for that 3 experiments,

or can I gather the 9 replicates to get the mean and standard deviation for the graph plotting?

From the information posted, the former seems to be the answer. I have tried both ways and it seems to give similar plot. However, the standard deviations may vary slightly.
Just want to clear my doubts.
Thanks

My opinion: The minimum number of experiments (n number) you can give a std error to is 2 since you divide by the squareroot of n-1.
You should not just sum up and divide all replicates but instead you should calculate the mean value for each experiment (in you case you would have 3 replicates of each experiment => 3 mean values). Then you use these values for calculating statistics (mean of means) and use the n number 3.

The question about statistics does not have a definite solution, people do as they like and as long as they write exactly what they have done, its all up to the referees...

Hope it helps

Thanks DLY