Table 2. Serum PSA level by age group (ng ml⁻¹).

Age group (years)	Number (%) of patients	PSA level (ng ml−1) (mean±s.d.)	P5	P25	P50	P75	P95
20–29	906 (13.4)	0.84±0.54*	0.30	0.50	0.70	1.02	1.79
30–39	2379 (35.1)	0.87±0.52*	0.31	0.51	0.75	1.07	1.85
40–49	3489 (51.5)	0.93±0.59*	0.32	0.54	0.78	1.15	2.09

Abbreviation: PSA, prostate-specific antigen.

*P<0.001, compared between each two age groups.