Dragan and wjt--your posts were very helpful and I used the equation to calculate standard deviation for the average of 3 samples with 3 replicate analyses each. I am reporting the results and was asked to use the equation in the report and also want to provide a citation.

Can I cite something formally and what should I refer to the result as that is understood by the statistical and scientific community? I have been referring to the value as the overall standard deviation, but is there a formal name? Is joint standard deviation used? I could not find a convention for naming this value and could not find this equation in any text book. I know these posts are going back awhile but I appreciate the help! I really need to provide a reference.