# Tagged Questions

compositional data and compositional data analysis, refers to varibles representing proportions, so non-negative and always summing up to one. See https://en.wikipedia.org/wiki/Compositional_data

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### Best way to analyse percentage data

I have percentage data and would like to see if these different variables have an affect on certain factors; i.e., I have different habitats of an area e.g., improved grassland: 40%, arable: 15%, ...
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### Sample from a multivariate distribution with contraints (Sand +Silt + Clay = 100 %)

I need to generate a sample from three distributions (I assume them Gaussian), respectively sand, silt, and clay. Actually, these variables are found in three soil maps. For each of them we have the ...
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### Eliminating noise / contamination in compositional data

I have data in compositional form. That is a matrix where the columns (each column is a sample) sum to 1. So, each element i,j in the matrix is the fraction of ...
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### Are crossplots of closed-sum attributes from independent analyses valid?

Some geochemistry papers that I have read contain crossplots of compositional components that resulted from different analyses of a rock sample. For example, one is the percent volume of TiO$_2$ ...
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### Visualizing composititional time series with negative values and meaningful totals

I have a compositional time series containing negative values, like this: ...
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### Multivariate data analyis of compositional data

Suppose I have a multivariate, compositional dataset that depicts the concentration of different elements. However, the data are not available on a single scale; i.e., some are of form 0.00x while ...
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### Which variables should I transform, center, and/or standardize in my data for Principal Component Analysis?

I have multiple datasets that I am attempting to use principal component analysis (PCA) on in order to infer the underlying structure of the data. I'm attempting to predict growth increment of ...
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### Finding mean and SD of 2 parts of a whole

I am putting together a review/meta-analysis of body composition in children. The data I will analyze consists of measures of fat-mass (FM) and fat-free-mass (FFM), which when summed equal total mass....
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### Analysing data measured as proportional composition

I have a data set on the proportional composition of marine substrate for different locations which I would like to compare. For example, one replicate transect within a location may be 50% sand, 25% ...