Column: Chemometrics in Spectroscopyhttp://www.spectroscopyonline.com/column-chemometrics-spectroscopy2018-03-24T15:12:51-04:00SpectroscopyOutliers, Part II: Pitfalls in Detecting Outliershttp://www.spectroscopyonline.com/outliers-part-ii-pitfalls-detecting-outliers
This column is part II of our series dealing with the question of outliers. Here we consider some of the methods that have been devised to detect the presence of an outlier when it is mixed in with multiple other, similar, samples.
Whether we did it well or badly, in the previous co2018-02-01T05:00:00+00:002018-02-21T17:30:08+00:00Calibration Transfer Chemometrics, Part I: Review of the Subjecthttp://www.spectroscopyonline.com/calibration-transfer-chemometrics-part-i-review-subject
Calibration transfer involves multiple strategies and mathematical techniques for applying a single calibration database consisting of samples, reference data, and calibration equations to two or more instruments. The instruments used for initial calibration development and transfer may be of 2017-10-01T04:00:00+00:002017-11-14T16:00:23+00:00Outliers, Part I: What Are Outliers?http://www.spectroscopyonline.com/outliers-part-i-what-are-outliers
This column is our attempt to make some sense out of what is fundamentally a very fuzzy notion. Since the twin sciences of statistics and chemometrics are firmly grounded in mathematics, there would seem to be no wiggle room for fuzziness in the results. However, the presence of nois2017-06-01T04:00:00+00:002017-06-13T13:30:09+00:00Bias and Slope Correctionhttp://www.spectroscopyonline.com/bias-and-slope-correction
As we have previously discussed, the most time consuming and bothersome issue associated with calibration modeling and the routine use of multivariate models for quantitative analysis in spectroscopy is the constant intercept (bias) and slope adjustments. These adjustments must be routinely pe2017-02-01T05:00:00+00:002017-02-13T22:01:32+00:00Statistics, Part III: Third Foundationhttp://www.spectroscopyonline.com/statistics-part-iii-third-foundation
Part III of this series discusses the principle of least squares.
This column is the continuation of our previous discussions dealing with statistics (1,2), and also presents a correction to that column. As we usually do, when we continue the discussion of a topic through more than 2016-11-01T04:00:00+00:002016-12-07T22:02:14+00:00How to Select the Appropriate Degrees of Freedom for Multivariate Calibrationhttp://www.spectroscopyonline.com/how-select-appropriate-degrees-freedom-multivariate-calibration
This column addresses the issue of degrees of freedom (df) for regression models. It seems there is some confusion about the use of df for the various calibration and prediction situations the standard error parameters should be comparable and are related to the total independent sampl2016-06-01T04:00:00+00:002016-06-17T15:02:03+00:00Statistics, Part II: Second Foundationhttp://www.spectroscopyonline.com/statistics-part-ii-second-foundation
This column is the continuation of our discussion in part I dealing with statistics.
This column is part II in our discussion dealing with statistics (1). As we usually do, when we continue the discussion of a topic through more than one column, we continue the numbe2016-02-01T05:00:00+00:002017-10-26T20:00:27+00:00Statistics, Part I: First Foundationhttp://www.spectroscopyonline.com/statistics-part-i-first-foundation
As a rejuvenation of a previous attempt to disseminate and promulgate correct statistical understanding and methodology, we present the first of a short set of columns dealing with the subject of statistics. This current series is organized as a top-down view of the subject, as opposed t2015-10-01T04:00:00+00:002017-11-10T15:30:09+00:00Optimizing the Regression Model: The Challenge of Intercept Bias and Slope Correction http://www.spectroscopyonline.com/optimizing-regression-model-challenge-intercept-bias-and-slope-correction
The archnemesis of calibration modeling and the routine use of multivariate models for quantitative analysis in spectroscopy is the confounded bias or slope adjustments that must be continually implemented to maintain calibration prediction accuracy over time. A perfectly developed calibrati2015-07-01T04:00:00+00:002017-11-20T15:30:44+00:00Choosing the Best Regression Modelhttp://www.spectroscopyonline.com/choosing-best-regression-model
When using any regression technique, either linear or nonlinear, there is a rational process that allows the researcher to select the best model. One question often arises: Which regression method (or model) is better or best when compared to others? This column discusses a mathematica2015-06-01T04:00:00+00:002017-10-26T20:00:33+00:00Units of Measure in Spectroscopy, Part III: Summary of Our Findingshttp://www.spectroscopyonline.com/units-measure-spectroscopy-part-iii-summary-our-findings
Volume 30 Number 2
Pages 24-33
What is it that we thought we knew that we have learned "ain't so" from the work reported in this series of columns?
This column is the next installment in our discussion of units of measure, an outgrowth of our discu2015-02-01T05:00:00+00:002017-09-29T14:34:53+00:00Calibration Transfer, Part VI: The Mathematics of Photometric Standards Used for Spectroscopyhttp://www.spectroscopyonline.com/calibration-transfer-part-vi-mathematics-photometric-standards-used-spectroscopy
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Photometric accuracy and precision, as reproducibility and repeatability, respectively, are essential for building consistent large databases over time for use in qualitative searches or quantitative multivariate analysis.2014-10-30T04:00:00+00:002017-10-26T20:00:40+00:00Units of Measure in Spectroscopy, Part II: What Does It Mean?http://www.spectroscopyonline.com/units-measure-spectroscopy-part-ii-what-does-it-mean
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Now that we have shown the relationships between different units for concentration, we continue by demonstrating their effects on the data we collected and used for our examples. We also begin our discussion on the ramific2014-09-01T04:00:00+00:002017-10-26T20:01:01+00:00Calibration Transfer, Part V: The Mathematics of Wavelength Standards Used for Spectroscopyhttp://www.spectroscopyonline.com/calibration-transfer-part-v-mathematics-wavelength-standards-used-spectroscopy
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How does one compute the mathematical certainty of wavelength standards used for calibrating instrumentation used for molecular spectroscopy measurements? This question becomes of major importance when the technique u2014-06-01T04:00:00+00:002017-10-26T20:01:12+00:00Units of Measure in Spectroscopy, Part I: It's the Volume, Folks!http://www.spectroscopyonline.com/units-measure-spectroscopy-part-i-its-volume-folks
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The data show that different units of measurement have different relationships to the spectral values, for reasons having nothing to do with the spectroscopy. This finding disproves the unstated, but near-un2014-02-14T05:00:00+00:002017-10-26T20:00:15+00:00Calibration Transfer, Part IV: Measuring the Agreement Between Instruments Following Calibration Transferhttp://www.spectroscopyonline.com/calibration-transfer-part-iv-measuring-agreement-between-instruments-following-calibration-transfer
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This is our 100th "Chemometrics in Spectroscopy" column, and when including "Statistics in Spectroscopy," there are now a total of 138 columns. We began in 1986 and have been working since that tim2013-10-01T04:00:00+00:002017-10-26T20:00:29+00:00Calibration Transfer, Part III: The Mathematical Aspectshttp://www.spectroscopyonline.com/calibration-transfer-part-iii-mathematical-aspects
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This column is a continuation from our previous two columns on the subject of multivariate calibration transfer (or calibration transfer) for spectroscopy. As we noted in the previous columns, calibration tr2013-06-01T04:00:00+00:002017-10-26T20:00:28+00:00Calibration Transfer, Part II: The Instrumentation Aspectshttp://www.spectroscopyonline.com/calibration-transfer-part-ii-instrumentation-aspects
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This is a continuation from our previous column on the subject of multivariate calibration transfer (or calibration transfer) for spectroscopy. As we noted in part I, calibration transfer is a seri2013-05-01T04:00:00+00:002017-11-10T15:00:21+00:00Calibration Transferhttp://www.spectroscopyonline.com/calibration-transfer-0
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The results we found from our previous subseries about classical least squares analysis provides the mechanism for understanding when and why calibration transfer can be done easily or when it will be difficult. Those resu2013-02-01T05:00:00+00:002017-10-26T20:00:39+00:00Classical Least Squares, Part XI: Comparison of Results from the Two Laboratories Continued, and Then the Light Dawnshttp://www.spectroscopyonline.com/classical-least-squares-part-xi-comparison-results-two-laboratories-continued-and-then-light-dawns
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Finding that the experiments performed in two different laboratories gave substantially the same results, we redoubled our efforts to determine the cause of the discrepancy between the spectral and reference conc2012-10-01T04:00:00+00:002017-10-26T20:00:50+00:00