To the Editor In their Editorial on evaluating data from observational research, Dr Goodman and colleagues1 mischaracterized the reasons for the apparent difference between the results of the Nurses’ Health Study (NHS) and the Women’s Health Initiative Trial (WHI) of hormone therapy (HT). The main reason for the difference was that in the observational studies, including the NHS, nearly all HT use began in early menopause (within a few years of onset), and most was estrogen alone, without progestin. Because coronary disease is uncommon in early menopause, the WHI targeted an older age group (mean age, 63 years [range, 50-79 years]) to increase statistical power. This created a deviation from the “like vs like” principle enunciated by Goodman and colleagues.1
Bhupathiraju SN, Stampfer MJ, Manson JE. Posing Causal Questions When Analyzing Observational Data. JAMA. 2017;318(2):201. doi:10.1001/jama.2017.6227
* * SCHEDULED MAINTENANCE * *
The JAMA Network Sites will be conducting routine maintenance from 10/20/2017 through 10/21/2017. During this window access to content and authentication may be intermittently available. The JAMA Store will be completely unavailable during the maintenance window.