ASCA: analysis of multivariate data from an experimental design, Biosystems Data Analysis group Universiteit van Amsterdam
Contents ANOVA SCA ASCA Conclusions
ANOVA different design factors contribute to the variation For two treatments A and B the total sum of squares can be split into several contributions
Example Experiment: Time: 6, 24 and 48 hours Experimental Design: Rats are given Bromobenzene that affects the liver Groups: 3 doses of BB Animals: 3 rats per dose per time point Vehicle group, Control group Rat 1 11 Rat 2 11 Rat 3 11 Rat 1 12 Rat 2 12 Rat 3 12 Rat 1 13 Rat 2 13 Rat 3 13 Rats 6 hours 24 hours 48 hours chemical shift (ppm) Measurements: NMR spectroscopy of urine
NMR Spectroscopy -Each type of H-atom has a specific Chemical shift -The peak height is number of H-atoms at this chemical shift = metabolite concentration -NMR measures ‘concentrations’ of different types of H- atoms
Different contributions time Time Animal time Dose time Trajectories Experimental Design
The Method I: ANOVA Constraints: time time time Data Individualihih Dose grouph Timek MeaningSymbol Estimates of these factors:
The Method II ANOVA is a Univariate technique x X Structured !
Multivariate Data NMR Spectroscopy Covariance between the variables ppm 6.01 ppm Or: Relationship between the columns of X X
The Method III: Principal Component Analysis 3D 2D … Imagine! 350D 2D !!! x x x 3 X Loading PC 1 Loading PC 2 loadingsscores residuals PC 1 PC 2 Scores
The Method IV: ANOVA and PCA ASCA Column spaces are Orthogonal E Parts of the data not explained by the component models
In Words: ASCA models the different contributions to the variation in the data ASCA takes the covariance between the variables into account ASCA gives a solution for the problem at hand.
Results I 40 % Time (Hours) Scores control vehicle low medium high
Results II Quantitative effect! No effect of vehicle Scores are in agreement with visual inspection Time (Hours) Scores control vehicle low medium high
Results III biomarkers chemical shift (ppm) Differences between submodels Interesting for Biology Interesting for Diagnostics Unique to the α submodel
Conclusions Metabolomics (and other –omics) techniques give multivariate datasets with an underlying experimental design For this type of data, ASCA can be used The results observed for this experiment are in accordance with clinical observations The metabolites that are responsible for this variation can be found using ASCA BIOMARKERS
Discussion 1.How can I perform statistics on the ASCA model? (e.g. Significance testing) 2.Are there other constraints possible for this model? (e.g. stochastic independence) 3.Are there alternative methods for solving this problem?