dataset-correlation.md

 # Correlation between datasets
 
+With molecules expressed as [signatures](signaturization), it becomes straightforward to assess the similarity principle, that is, it is easy to check whether similar molecules in a particular dataset are still similar in another dataset.
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+As of today, we measure the following types of correlation (only between the 25 exemplary datasets):
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+* Canonical correlation analysis.
+* Shared pairs of similar molecules.
+* Coincidence of similarity ranks.
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+These correlations are used not only for analysis, but more importantly, to *predict* unseen similarities. If two molecules are similar in a certain space, they are likely to be similar in other highly correlated spaces, too.
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+This approach yields predictors that are, hopefully, of sufficient quality for the [CC web app](http://chemicalchecker.org). However, I do think we have to be more ambitious and aim at more proficient classifiers, potentially using deep learning (e.g. siamese networks).
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+This will be a crucial achievement for the development of the CC as it will yield signatures of type 3, which are currently lacking.
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