Table A Pairwise distribution of twins by site of osteoporotic fracture in Finnish twin cohort*
 

Detail	Total No of pairs	Fracture cases	Overall cumulative fracture risk† (95% CI)	Discordant pairs (D)	Concordant pairs (C)	Pairwise concordance‡ (95% CI)	Probandwise concordance§ (95% CI)	Relative fracture risk ¶ (95% CI)
Hip
MZ	2308	111	0.024 (0.020 to 0.029)	95	8	0.078 (0.034 to 0.15)	0.144 (0.055 to 0.23)	5.99 (3.68 to 9.78)
DZ	5241	190	0.018 (0.016 to 0.021)	166	12	0.067 (0.035 to 0.12)	0.126 (0.062 to 0.19)	6.97 (4.67 to 10.4)
Pelvis, knee, and ankle
MZ	2308	92	0.020 (0.016 to 0.024)	88	2	0.022 (0.003 to 0.078)	0.043 (!0.015 to 0.10)	2.18 (0.82 to 5.81)
DZ	5241	213	0.020 (0.018 to 0.023)	205	4	0.019 (0.005 to 0.048)	0.038 (0.002 to 0.073)	1.85 (0.93 to 3.69)
Proximal and distal humerus and wrist
MZ	2308	36	0.008 (0.005 to 0.010)	36	0	0	0	0
DZ	5241	98	0.009 (0.008 to 0.011)	98	0	0	0	0
Spine and ribs
MZ	2308	26	0.006 (0.004 to 0.008)	24	1	0.040 (0.001 to 0.20)	0.077 (-0.065 to 0.22)	13.7 (3.4 to 55)
DZ	5241	87	0.008 (0.007 to 0.010)	85	1	0.012 (0.003 to 0.063)	0.023 (-0.021 to 0.067)	2.77 (0.69 to 11.1)

*All subjects with osteoporotic fracture, as identified from Finnish hospital discharge register in 1972­96, were included. In calculation of concordant pairs for each fracture group, only fractures similar to fractures in that particular group were included–that is, in hip fractures only twin pairs in whom both cotwins in pair had hip fracture were registered as concordant pairs.

†Overall cumulative risk is calculated by dividing number of fracture cases by total number of individuals for–example, on first row of table 111/2÷2308=0.024

‡Pairwise concordance is calculated by formula of C/C+DC for example, on first row of table 8/103=0.078.

§Probandwise concordance is calculated by formula of 2C/(2C+D)C for example, on first row of table 2÷8/(2÷8+95)=0.144.

¶Relative fracture risk is calculated by dividing probandwise concordance by overall cumulative fracture risk–for example, on first row of table 0.144/0.024=6.00.

MZ=monozygotic; DZ=dizygotic.