Table 1.

Category of errors before and after 2000

Category	Retractions (n)		Total [n (%)]	P
	Pre-2000	Post-2000
Irreproducibility	38	30	68 (16.1)	0.0017
Laboratory error	97	139	236 (55.8)	0.2293
Unique	43	85	128 (54.2)	0.0119
Contamination	44	30	74 (31.3)	0.0002
DNA-related	8	22	30 (12.7)	0.1118
Control	2	2	4 (1.7)	0.6411
Analytical error	20	60	80 (18.9)	0.0071
Other	8	31	39 (9.2)	0.0155
Total	163	260	423

P values calculated by 2-tailed Fisher's exact test using raw numbers of retracted papers.