Three levels of quality were defined in the data: high, medium, and low. Data from the difference sources were all classified in one of these three classifications. ChEMBL version 29 (ChEMBL29) data were first split between high and low quality data In total 18,635,916 activity data points measured on 2,105,464 compounds and 14,554 targets were extracted. The following data were deemed as low quality: Data flagged as potential duplicates, of questioned validity (Supplementary Table ) -unless errors were confirmed by authors, in which case they were entirely disregarded -, censored, not associated with any pChEMBL value, or of questioned activity (Supplementary Table ). Remaining activity data were temporarily regarded as high quality. In the ExCAPE-DB dataset , if the data source was PubChem (source identifier 7), then the data was flagged as high quality. Protein targets were retrieved along with their classifications if they had Uniprot 18 accessions defined. Accession Q8MMZ4, corresponding to the secondary accession for the Plasmodium falciparum (isolate NF54) cGMP-dependent protein kinase was associated with a secondary UniProt accession and was manually replaced by its primary accession Q8MMZ4. Using accessions, protein sequences were then obtained from UniProt. Only molecules identified as small molecules and associated with a molecular registry number were kept, then parsed from connection tables and standardised (see Molecular structure standardisation). Activity data of high quality were reclassified as low quality if the target type was other than 'single protein' or the assay confidence score was 0, 1, 2, 3, 4 or 6 (Supplementary Table ). Activity data with assay confidence scores of 5 and 8 were reclassified of medium quality.