Charlie Saunders writes:
A study has recently been published in the New England Journal of Medicine (NEJM) which uses survival analysis to examine long-acting reversible contraception (e.g. intrauterine devices [IUDs]) vs. short-term commonly prescribed methods of contraception (e.g. oral contraceptive pills) on unintended pregnancies.
The authors use a convenience sample of over 7,000 women. I am not well versed-enough in sampling theory to determine the appropriateness of this but it would seem that the use of a non-probability sampling would be a significant drawback. If you could give me your opinion on this, I would appreciate it.
The NEJM is one of the top medical journals in the country. Could this type of sampling method coupled with this method of analysis be published in a journal like JASA?
My reply: There are two concerns, first that it is a convenience sample and thus not representative of the population, and second that the treatments are chosen rather than randomly assigned, hence there will be pre-treatment differences between the groups. That said, perhaps this descriptive information is valuable. From a statistical perspective, the strengths of the study are realism of the conditions and accuracy of the measurements.