Reducing the risk of fractures with calcium and vitamin DBMJ 2010; 340 doi: https://doi.org/10.1136/bmj.b5492 (Published 13 January 2010) Cite this as: BMJ 2010;340:b5492
All rapid responses
Erratum - Reduction in hip fracture risk was statistically significant, but underestimated in the CaD trials subanalysis due to coding error
We have posted the following rapid reponse to the article that this
editorial refers to:
To the editor of BMJ
Dear Dr Godlee,
Regarding our paper "Patient level pooled analysis of 68 500 patients
from seven major vitamin D fracture trials in US and Europe", published in
BMJ 2010 (BMJ. 2010 Jan 12;340:b5463.).
In subsequent work using the DIPART dataset we have become aware of a
coding error that led to a modest underestimation in the BMJ paper of the
reduction in hip fracture risk for vitamin D supplements given with
For one of the studies (the Porthouse study) there was a coding error
when importing the treatment allocation variable, so that participants
allocated to no treatment were considered in the analysis as being on
calcium and vitamin D supplements and vice versa. The results have been
strengthened slightly by correcting this error and the reduction in hip
fracture risk is now statistically significant. All results pertaining to
vitamin D given without calcium are unaffected.
In figure 3 we reported a hazard ratio, HR for the any fracture
outcome of 0.95 (95% confidence interval, CI 0.90-1.01) for all trials,
0.92 (0.86-0.99) for CaD trials and 1.01 (0.92-1.12) for D trials. These
results were all unaffected by correcting the treatment status coding for
the Porthouse trial.
In figure 4 we reported a HR for the hip fracture outcome of 0.97
(0.86-1.10) for all trials, 0.84 (0.70-1.01) for CaD trials and 1.09 (0.92
-1.29) for D trials. After correcting the coding error, the HR for all
trials combined was 0.96 (0.85-1.09) while the effect in the CaD trials
became statistically significant with an HR of 0.83 (0.69-0.99). Again, D
trials were not affected by the miscoding.
In table 2 we reported a subanalysis that found a HR for the 20ug
vitamin D dose given with calcium of HR 0.95 (0.80 to 1.14) for any
fracture, HR 1.30 (0.88 to 1.92) for hip fracture and HR 0.97 (0.48 to
1.98) for vertebral fracture. The correct risk hazard ratios are HR 0.99
(0.84 to 1.19), HR 1.19 (0.81 to 1.75) and HR 0.99 (0.49 to 2.04). All
other hazard ratios in the table are correct as stated and there are no
alterations to the conclusions of the subanalysis.
After correction, the absolute hip fracture risk reduction was 0.4%
for participants aged over 70 and 0.2% in participants with previous
fractures, giving numbers needed to treat (NNT) of 250 and 524 (not 255
and 548). The NNT for all fractures was correct as reported.
On behalf of the DIPART authors, I wanted to make you aware of this
coding error. The change in effect size is very small and the conclusions
still hold as reported. However, we understated the treatment effect on
hip fractures, which is in fact statistically significant. We would be
grateful if these corrections could be published as an erratum to the
paper as soon as practicable. If desired, we can supply revised tables or
the erratum could simply consist of the text in bold above
Competing interests: Grant / Research support from Novartis, Nycomed, Amgen, Merck Speakers Bureau with Nycomed, Merck, Eli Lilly.