Basic Statistics and Data Handling

How many samples do we need to collect for a given analysis How large must the sample be to insure that it is representative These types of questions can be answered by statistics. We also need to have a basic knowledge of statistics to understand the limitations in the other steps in method development, so we will now briefly introduce the statistical concepts and calculations used by analytical chemists. 

In order to design the correct experiment to answer the analytical question being asked, statistical methods are needed to select the size of the sample required, the number of samples, and the number of measurements that must be performed to obtain the needed accuracy and precision in the results generated by the experiment. Statistical analysis of data is also used to express the uncertainty in measured values, so that the users of the data understand the limitations associated with results. Every measured result has uncertainty associated with it it is part of the analyst s job to express that uncertainty in a way that defines the range of values that are reasonable for the measured quantity. Uncertainty, properly evaluated and reported with the measured value, indicates the level of confidence (CL) that the value actually lies within the range reported. 

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