Number of hip fractures in untreated women with osteoporosis
No risk factors:
(5-year probability of hip fracture in women with osteoporosis) x (prevalence of osteoporosis) x N
At least one risk factor:
1.7 x (5-year probability of hip fracture in women with osteoporosis) x (prevalence of osteoporosis) x N
Number of hip fractures in treated women with osteoporosis
No risk factors:
(RR for hip fracture from treatment trials) x (0.7 adherence) x (number of hip fractures in untreated women with osteoporosis) + (1 - 0.7 adherence) x (number of hip fractures in untreated women with osteoporosis)
At least one risk factor:
(RR for hip fracture from treatment trials) x (0.7 adherence) x (number of hip fractures in untreated women with osteoporosis with at least one risk factor) + (1 - 0.7 adherence) x (number of hip fractures in untreated women with osteoporosis with at least one risk factor)
Number-needed-to-screen for benefit
N / (number of hip fractures without treatment - number with treatment)
Number-needed-to-treat
Number of women with osteoporosis / (number of hip fractures without treatment - number with treatment)