Table 4.

 Risk factors for kidney stones and urinary tract stones among the patients. Values are risk estimates (95% confidence intervals)

Variable	Unadjusted odds ratio			Adjusted risk estimate
	Before surgery	After surgery		Before surgery†	After surgery‡
Age (⩾60 v <60 years)	0.34 (0.22 to 0.52)*	0.28 (0.15 to 0.54)*		0.33 (0.20 to 0.54)*	0.44 (0.20 to 0.96)*
Preoperative stones (yes/no)	—	11.13 (6.50 to 19.08)*		—	5.89 (3.04 to 11.41)*
Weight of diseased tissue (⩾1g v <1 g)	1.05 (0.67 to 1.64)	1.05 (0.56 to 1.98)		0.91 (0.56 to 1.48)	1.03 (0.54 to 1.96)
Sex (male/female)	2.02 (1.31 to 3.11)*	2.63 (1.46 to 4.75)*		1.83 (1.11 to 3.00)*	1.51 (0.79 to 2.92)
Serum ionised calcium (>1.55 mmol/l v ⩽1.55 mmol/l)§	0.91 (0.59 to 1.40)	0.97 (0.52 to 1.81)		1.09 (0.67 to 1.78)	0.86 (0.45 to 1.65)

^*P<0.05. 

^†Logistic regression (odds ratio). 

^‡Cox regression (hazard ratio). 

^§Measured the day before surgery.