Question

Deciding how to manipulate samples and how many measurements must be made are often determined by the precision required in the final result. Consider the situation with 50 total samples taken from a stream. For this exercise, one may assume all 50 samples have the same composition. The sampling standard deviation (i.e. the variation due strictly to measuring different samples) is 0.3 μg/mL, while the mean value of the analyte concentration to be measured is 7.20 μg/mL. The standard deviation of a single analytical measurement on this type of sample is 0.4 μg/mL, and is independent of sample size for samples the size of each of these 50 samples or for larger samples. But the standard deviation of a single analytical measurement increases as the sample is made smaller each of these 50 samples.

Describe a general, economical method of lowering the total variance significantly from the result obtained on a single sample. How does one decide how many samples must be measured?

Answer 1