Category Archives: Statistics

Analysis of Pb in Biological and Environmental Samples

A paper by Yan, et. al. [Yan, X.-P.; Sperling, M.; Welz, B. Anal. Chem. 1999, 71, 4216-4222] describes a newly developed analytical method for the analysis of biological and environmental samples containing Pb2+ in the presence of a variety of … Continue reading

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Analysis of a Digital Pipet

Mechanical micropipets are commonly used to dispense small (μL) volumes of reagents.  A recent “Application Note” [Am. Lab. June 1999] contains the following data for 50 replicate deliveries of a reagent using a 5.0-μL micropipet. Average volume delivered = 4.967 … Continue reading

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Determination of Fat in a Snickers’ Bar

In a recent paper [J. Chem. Educ. 1997, 74, 1108-1111], Snow, Dunn and Patel describe the experimental determination of fat in a SnickersTM candy bar.  The fat was removed by extraction with supercritical CO2, with the sample weighed before and … Continue reading

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Comparison of Glucometers

A glucometer is a portable device used to monitor glucose levels in blood.  Of concern for users is repeatability between units of the same model, or between different models.  The following data [from Edminston, P. L.; Williams, T. R. J. … Continue reading

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Spike Recovery for Analysis of Ginkgolide

One concern in any analysis is the impact of the sample’s matrix.  A method for an analyte that is known to work well in one matrix may yield problems when applied to a sample with a different matrix.  One way … Continue reading

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What is the Difference Between Repeatability, Reproducibility, Accuracy, and Precision?

In an editorial published in American Laboratory (November 2000), Ira S. Krull states that in “any science, then, one must present at the very outset evidence of repeatability, reproducibility, accuracy, and precision (emphasis added).” Suppose you are preparing a manuscript … Continue reading

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NIST Statistics Problem

Have you ever wondered how atomic weights are determined? The National Institute of Standards and Technology (NIST) is one of several research organizations that seeks to make accurate measurements of this sort. The most common approach is to prepare a … Continue reading

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