Table 1.

Numbers of proteins by neXtProt protein existence (PE) evidence levels from 2012–02 to 2023–04, showing progress in identifying PE2,3,4 missing proteins to become PE1 proteins and PeptideAtlas canonical proteins by mass spectrometry.^a,b,c

PE Level	2012–02	2013–09	2014–10	2016–01	2017–01	2019–01	2020–01	2021–02	2022–02	2023–04
1:Evidence at protein level	13,975	15,646	16,491	16,518	17,008	17,694	17,874	18,357	18,407	18,397
2:Evidence at transcript level	5205	3570	2647	2290	1939	1548	1596	1265	1135	1151
3:Inferred from homology	218	187	214	565	563	510	253	147	195	215
4:Predicted	88	87	87	94	77	71	50	9	13	15
MP = PE2 + PE3 + PE4	5511	3844	2948	2949	2579	2129	1899	1421	1343	1381
Human PeptideAtlas canonical proteins	12,509	13,377	14,928	14,569	15,173	16,293	16,655	16,702	16,957	17,245

^aPE1/PE1+2+3+4 = 18,397/19,778 = 93.0%

^bPE 2+3+4 = 1381 “missing proteins” as of 2023–04.

^cMore stringent HPP Guidelines were imposed in 2016 and enhanced in 2019 ^{14, 15}