Questions tagged [chemometrics]
statistics used in chemistry.
117 questions
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How small a quantity should be added to x to avoid taking the log of zero?
I have analysed my data as they are. Now I want to look at my analyses after taking the log of all variables. Many variables contain many zeros. Therefore I add a small quantity to avoid taking the ...
- 3,894
35
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2
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When if ever is a median statistic a sufficient statistic?
I came across a casual remark on The Chemical Statistician that a sample median could often be a choice for a sufficient statistic but, besides the obvious case of one or two observations where it ...
- 110k
8
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3
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Appropriate approach for checking concentration change for 80 substances with n = 3 for three time points
I am relatively new to statistics and would appreciate some guidance on whether my analysis approach is appropriate.
What I have:
I measured concentrations of 80 different substances. There are three ...
- 81
8
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1
answer
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Mean centering or not in the context of Partial Least Squares
In my current project, I'm using PLS regression on infrared spectra (FTIR). For this I'm using R and the pls function from the plsr package. ...
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7
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2
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Exclude observations with measurements below limit of detection?
I am analysing a dataset for the relationship between an exposure variable x and a response y (in my case, these are urinary ...
- 355
7
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1
answer
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How to predict a binary outcome with unbalanced repeated measures data?
I’m somewhat lost as to how to approach a problem I have and was hoping someone can suggest the most appropriate method.
The problem:
I have a data set consisting of concentration values for 8 ...
- 151
7
votes
1
answer
381
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Determining whether new data is "in distribution" with training data
I'm hoping to use machine learning to predict chemical properties of various molecules. Many chemistry machine learning research papers that I come across talk about model generalizability issues ...
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5
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2
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Predicting chemical property (Boiling Point) from a SMILES string
I was trying to develop a model for predicting Boiling Points (BP) given a chemical name. One good and unique (ok, almost) way to encode a name is the SMILES notation string. The details of the ...
- 1,101
5
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1
answer
617
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Is removing points from a calibration rigorous?
When a calibration is generated from a set of standards run on an analytical instrument, should the standards be remade and reanalyzed if not all of the points fit within 20%-30% (depending on ...
- 10.2k
5
votes
1
answer
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statistical handling of lab values below limit of quantitation (BLQ)
There were several samples BLQ because of the lower limit of quantitation (LLQ) of the method, e.g. 5 ng/ml or less. Using the statistical program PRISM6 I marked these values together with the ...
- 51
5
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1
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Should I use the prediction interval or inverse prediction interval to calculate the uncertainty of $x$ when using reverse regression?
I'm calibrating a piece of lab instrumentation. I create solutions of known concentration ($x$) and measure my instrument response ($y$). On unknown samples, I measure the response and use the ...
- 618
5
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0
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Is there an alternate $\chi^2$ calculation useful for data spanning a large scale?
I have experimental small angle scattering data which provide information about the structure of a molecule. I can use a PDB file of a molecular structure (contains all the atom names and coordinates)...
- 391
4
votes
2
answers
141
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Logistic regression modeling of molecule conversion
A recent question addressed a regression where a chemical was treated with a mixture having a particular concentration, to see the proportion of the chemical that converted to a new substance.
The ...
- 73.7k
4
votes
1
answer
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Prediction of independent data with PLS
In Matlab's plsregress function and in many other statistic toolboxes, there is a BETA vector returned that simplyfies the regression problem to(excluding the ...
- 1,542
4
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1
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How is "Orthogonal distance" computed?
I was reading the vignette of the R package chemometrics (link). In the second paragraph (right below the first equation) of Page 12, the author writes:
the OD (...
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