For more than a decade, drug-eluting stents (DES) have been the mainstay for the treatment of coronary artery disease. Technology advancements of DES have been particularly relevant over the last few years and have resulted in increased safety and efficacy of newer-generation vs early-generation DES, as several randomised trials and meta-analyses have documented [1] [2] . Anyway, the data for safety and efficacy of DES in women are sparse because their inclusion in randomised clinical trials is generally limited [1] .

On the other hand, recent studies, particularly in the field of pharmacotherapy have addressed the question of whether or not the incremental benefits found in randomized trials are consistent with the expected outcomes that are pre-declared in statistical power calculations of the trials [3] [4] . In particular, a comparison has been proposed between the pre-specified “delta” (or margin) declared in the statistical power section of the trials and the real incremental benefit observed thereafter from the trial’s results (or meta-analyses). These margins, that are assumed to identify a threshold between clinically relevant benefits and irrelevant ones, can be handled in the framework of equivalence tests, and equivalence corresponds to demonstrating the proof of no difference.

In this report, we describe the application of this type of analysis for interpreting the incremental benefit of newer-generation vs early-generation DES in women receiving percutaneous coronary intervention.

Our clinical material was obtained from the meta-analysis by Stefanini et al. [1] who studied this specific comparison according to the end-point of target-lesion revascularisation (TLR), The crude rates of TLR for newergeneration DES and early-generation DES were, respectively, 236/6278 (3.76%) vs 205/4171 (4.91%) at 1 year and 330/6278 (5.26%) vs 294/4171 (7.05%) at 3 years. These findings generate a rate difference (RD) for TLR of −1.16% at 1 year [95% confidence interval (CI): −1.96% to −0.35%] and of −1.79% at 3 years (95% CI: −2.75% to −0.84%) in favour of newer-generation DES. To apply the equivalence testing to these findings, we sought information on the margins in previous trials conducted on this topic; Stone et al. [2] adopted the endpoint of TLR in their trial comparing everolimus-eluting vs paclitaxel-eluting stents and employed a margin of ±2.9% expressed as RD. Any difference within the limit of 2.9% in TLR rates can therefore be assumed to identify an equivalence interval; other randomized studies in this area have generally adopted wider margins (between 3% and 4%). Hence, our equivalence test [5] was designed to combine the values of RD found by Stefanini et al. [1] with the margins adopted by Stone et al. [2] .

Our results, based on the end-point of TLR, are summarized in Figure 1. The Forest plot clearly shows that, in women, there is an equivalent effectiveness between newer-generation and early-generation DES.

Since the interpretation made by Stefanini et al. [1] of their results was that the newer-generation of DES is more effective than the early-generation one, and this issue deserves a close scrutiny. As pointed out by Ahn et al. [5] , when a specific data set indicates, at the same time, equivalence and superiority, the interpretation is controversial, and two different hypotheses can be proposed. First, equivalence margins were too wide, and so superiority should prevail in the interpretation. Second, the margins were reasonable, so the conclusions should favour equivalence. In this specific case, we think that priority should be given to equivalence rather than to superiority.

None declared.

The authors have carried out this study in the context of their activity at the above mentioned institution; ESTAV Centro belongs to the Italian national health system.