Table 4.

Multivariate negative binomial model for the monetary value of payments on an individual basis

Variable	All (n=1080) Relative monetary value per year (95% CI)	Low-payment and no-payment groups (0–1 million yen (£6800)) (n=938) Relative monetary value per year (95% CI)
Sex
Men	Ref.	Ref.
Women	0.40 (0.20 to 0.79)**	0.40 (0.28 to 0.58)***
Types of affiliations
Other type of institutions	Ref.	Ref.
University hospitals	5.78 (3.34 to 10.02)***	1.08 (0.80 to 1.47)
Cancer hospitals	5.47 (3.30 to 9.06)***	1.11 (0.90 to 1.37)
Working region
Kanto	Ref.	Ref.
Hokkaido	0.45 (0.16 to 1.26)	0.82 (0.54 to 1.23)
Tohoku	1.41 (0.62 to 3.20)	1.07 (0.69 to 1.67)
Chubu	0.86 (0.41 to 1.81)	0.96 (0.72 to 1.29)
Kinki	1.14 (0.66 to 1.96)	0.74 (0.54 to 1.03)
Chugoku	1.47 (0.50 to 4.32)	0.80 (0.53 to 1.22)
Shikoku	0.69 (0.32 to 1.53)	1.22 (0.78 to 1.89)
Kyushu	1.18 (0.55 to 2.51)	1.04 (0.74 to 1.45)
Year of experience after the board certification	1.40 (1.30 to 1.50)***	1.13 (1.09 to 1.17)***
Subspecialty
Respirology	Ref.	Ref.
Gastroenterology	0.57 (0.32 to 1.01)	0.94 (0.72 to 1.22)
Haematology	0.49 (0.30 to 0.83)**	0.76 (0.57 to 1.00)*
Breast	1.50 (0.68 to 3.33)	0.73 (0.45 to 1.19)
Other or undetermined*	0.28 (0.12 to 0.64)**	0.69 (0.51 to 0.93)*

*Other or undetermined specialties included head and neck cancer, gynaecology, urology and dermatology. Due to the small number of physicians in these four specialties, they were included in the ‘other or undetermined’ category; *<0.05, **<0.01, ***<0.001.