Frequently Asked Questions
The Infometrix Forum has many more tips for using Pirouette and other Infometrix products.
What reference books on chemometrics can you suggest?
- Beebe, Pell and Seasholtz: As a practical guide to applications in the chemical industry, this book steps through the chemometrics approach and spans many of the approaches seen in Pirouette.
- The Pirouette manual: Although not formally a book, this PDF is free and covers a lot of the basics for chemometrics. There are walkthroughs for both regression and classification analysis and a mathematical summary of all of the common techniques.
- Massart, Vandeginste, et al.: For the more adventurous, the Massart book is a complete and well-written tome that provides references to more cutting edge applications.
- Martens and Nęs: For those seeking detail on the mathematics of multivariate regression, this book is the most complete reference.
- Brown: not really a book, but a good introductory resource, A Short Primer on Chemometrics for Spectroscopists.
- A more extensive list of recommended reading....
For information on obtaining these texts, as well as for other fundamental publications, see the Resources page.
How do I choose among the Pirouette algorithms?
Our philosophy is to provide more than one algorithm to do any given task. For example, it is advisable to run both PCA and HCA when conducting an exploratory analysis of your data.
- Because PCA has the same factor basis as the other modeling algorithms (such as SIMCA and PLS), it should always be run as part of exploratory data analysis.
- Choosing between SIMCA and KNN is a function of the number of data points and their distribution; if clusters are reasonably separated and well-populated, SIMCA is the better choice in that it supplies outlier diagnostics.
- In regression, PLS usually models data with fewer factors than PCR because it assumes that there is some measurement error in the Y-block, usually the case.
- In mixture analysis, ALS is our preferred route in that the alternate (MCR) is restricted to 2 components, and ALS covers the most common closure constraints. ALS is weaker when you do not have samples that are relatively pure representatives of the end-members, a case for which MCR is better suited.
How do I get data into Pirouette from a source that Pirouette does not directly support?
Although Pirouette attempts to support the more common analytical file formats, we do not cover them all. Best is to look at your instrument system and see if it offers a means of saving some sort of standardized file format. In spectroscopy, this usually means the Galactic .SPC form or, a less consistently implemented standard, JCAMP. In chromatography, the AIA format is preferred and is fairly ubiquitous. If those still do not suit the needs, ASCII or Excel formats are accepted within Pirouette. Check the format options in the Pirouette manual (Chapter 14), and be aware that the Excel 256 column limitation often means that the exported data will contain samples in column orientation; you will need to transpose them once in Pirouette.
How can I capture a spinning 3D graphic for use in a PowerPoint presentation?
See this topic in the Infometrix forum.
Printing a dendrogram of a large number of samples may produce several pieces of paper that you need to paste together to make one continuous graphic. Take advantage of the continuous roll printers available in service bureaus with this procedure that makes a custom PDF file of your dendrogram.
Some data sources, for example, spectroscopy data systems, write text files in which the sample values are stored in columns. If there are more than 255 values, you cannot use a spreadsheet to transpose the data before reading into Pirouette because of the limit on number of spreadsheet columns. You can, however, configure the text file so that on reading into Pirouette, it will read columnar data into row format.
Although the newest Macintosh computers are now running on Intel processors, the Pirouette code base has not been optimized for this platform. However, you can still run Pirouette, and other Infometrix products, on a Mac by using Virtual PC. Here is a brief report on how to run Pirouette on a Mac.