On 2017 May 09, Kenneth J Rothman commented:

Lappe et al. (1) reported that women receiving vitamin D and calcium supplementation had 30% lower cancer risk than women receiving placebo after four years (hazard ratio (HR)=0.70, 95% confidence interval (CI): 0.47 to 1.02). Remarkably, they interpreted this result as indicating no effect. So did the authors of the accompanying editorial (2), who described the 30% lower risk for cancer as “the absence of a clear benefit,” because the P-value was 0.06. Given the expected bias toward a null result in a trial that comes from non-adherence coupled with an intent-to-treat analysis (3), the interpretation of the authors and editorialists is perplexing. The warning issued last year by the American Statistical Association (ASA) (4) about this type of misinterpretation of data should be embraced by researchers and journal editors. In particular, the ASA stated: “Scientific conclusions …should not be based only on whether a p-value passes a specific threshold.” Editors in particular ought to guide their readership and the public at large to avoid such mistakes and foster more responsible interpretation of medical research.

EE Hatch, LA Wise

Boston University School of Public Health

KJ Rothman

Research Triangle Institute & Boston University School of Public Health

References

(1) Lappe J,Watson P, Travers-Gustafson D, et al. Effect of vitamin D and calcium supplementation on cancer incidence in older women. JAMA. 2017; 317:1234-1243. doi:10.1001/jama.2017.2115

(2) Manson JE, Bassuk SS, Buring JE. Vitamin D, Calcium, and Cancer. Approaching Daylight? JAMA 2017; 317:1217-1218.

(3) Rothman KJ. Six persistent research misconceptions. J Gen Intern Med 2014; 29:1060-1064. doi: 10.1007/s11606-013-2755-z

(4) ASA statement on statistical significance and P-values. Am Stat. 2016. doi:10.1080/ 00031305.2016.1154108.

On 2017 May 09, Kenneth J Rothman commented:

Lappe et al. (1) reported that women receiving vitamin D and calcium supplementation had 30% lower cancer risk than women receiving placebo after four years (hazard ratio (HR)=0.70, 95% confidence interval (CI): 0.47 to 1.02). Remarkably, they interpreted this result as indicating no effect. So did the authors of the accompanying editorial (2), who described the 30% lower risk for cancer as “the absence of a clear benefit,” because the P-value was 0.06. Given the expected bias toward a null result in a trial that comes from non-adherence coupled with an intent-to-treat analysis (3), the interpretation of the authors and editorialists is perplexing. The warning issued last year by the American Statistical Association (ASA) (4) about this type of misinterpretation of data should be embraced by researchers and journal editors. In particular, the ASA stated: “Scientific conclusions …should not be based only on whether a p-value passes a specific threshold.” Editors in particular ought to guide their readership and the public at large to avoid such mistakes and foster more responsible interpretation of medical research.

EE Hatch, LA Wise

Boston University School of Public Health

KJ Rothman

Research Triangle Institute & Boston University School of Public Health

References

(1) Lappe J,Watson P, Travers-Gustafson D, et al. Effect of vitamin D and calcium supplementation on cancer incidence in older women. JAMA. 2017; 317:1234-1243. doi:10.1001/jama.2017.2115

(2) Manson JE, Bassuk SS, Buring JE. Vitamin D, Calcium, and Cancer. Approaching Daylight? JAMA 2017; 317:1217-1218.

(3) Rothman KJ. Six persistent research misconceptions. J Gen Intern Med 2014; 29:1060-1064. doi: 10.1007/s11606-013-2755-z

(4) ASA statement on statistical significance and P-values. Am Stat. 2016. doi:10.1080/ 00031305.2016.1154108.