Current controversies: Null hypothesis significance testing

Traditional null hypothesis significance testing (NHST) incorporating the critical level of significance of 0.05 has become the cornerstone of decision-making in health care, and nowhere less so than in obstetric and gynecological research. However, such practice is controversial. In particular, it was never intended for clinical significance to be inferred from statistical significance. The inference of clinical importance based on statistical significance (p < 0.05), and lack of clinical significance otherwise (p ≥ 0.05) represents misunderstanding of the original purpose of NHST. Furthermore, the limitations of NHST—sensitivity to sample size, plus type I and II errors—are frequently ignored. Therefore, decision-making based on NHST has the potential for recurrent false claims about the effectiveness of interventions or importance of exposure to risk factors, or dismissal of important ones. This commentary presents the history behind NHST along with the limitations that modern-day NHST presents, and suggests that a statistics reform regarding NHST be considered

Association between coffee or caffeine consumption and fecundity and fertility: a systematic review and dose&ndash;response meta-analysis

Julie Lyngs&oslash;,1 Cecilia H&oslash;st Ramlau-Hansen,1 Bj&oslash;rn Bay,2 Hans Jakob Ingerslev,3 Adam Hulman,1,4 Ulrik Schi&oslash;ler Kesmodel5 1Department of Public Health, Section for Epidemiology, Aarhus University, Aarhus, 2The Fertility Clinic, Regional Horsens Hospital, Horsens, 3Department of Obstetrics and Gynaecology, Aarhus University Hospital, Aarhus, 4Danish Diabetes Academy, Odense, 5Department of Obstetrics and Gynaecology, Herlev and Gentofte Hospital, Herlev, Denmark Objective: The aim was to investigate whether coffee or caffeine consumption is associated with reproductive endpoints among women with natural fertility (ie, time to pregnancy [TTP] and spontaneous abortion [SAB]) and among women in fertility treatment (ie, clinical pregnancy rate or live birth rate). Design: This study was a systematic review and dose&ndash;response meta-analysis including data from case&ndash;control and cohort studies. Methods: An extensive literature search was conducted in MEDLINE and Embase, with no time and language restrictions. Also, reference lists were searched manually. Two independent reviewers assessed the manuscript quality using the Newcastle&ndash;Ottawa Scale (NOS). A two-stage dose&ndash;response meta-analysis was applied to assess a potential association between coffee/caffeine consumption and the outcomes: TTP, SAB, clinical pregnancy, and live birth. Heterogeneity between studies was assessed using Cochrane Q-test and I2 statistics. Publication bias was assessed using Egger&rsquo;s regression test. Results: The pooled results showed that coffee/caffeine consumption is associated with a significantly increased risk of SAB for 300 mg caffeine/day (relative risk [RR]: 1.37, 95% confidence interval [95% CI]: 1.19; 1.57) and for 600 mg caffeine/day (RR: 2.32, 95% CI: 1.62; 3.31). No association was found between coffee/caffeine consumption and outcomes of fertility treatment (based on two studies). No clear association was found between exposure to coffee/caffeine and natural fertility as measured by fecundability odds ratio (based on three studies) or waiting TTP (based on two studies). Conclusion: Results from this meta-analysis support the growing evidence of an association between coffee/caffeine intake and the risk of SAB. However, viewing the reproductive capacity in a broader perspective, there seems to be little, if any, association between coffee/caffeine consumption and fecundity. In general, results from this study are supportive of a precautionary principle advised by health organizations such as European Food Safety Authority (EFSA) and World Health Organization (WHO), although the advised limit of a maximum of two to three cups of coffee/200&ndash;300 mg caffeine per day may be too high. Keywords: coffee, caffeine, fecundity, fertility, spontaneous abortion, assisted reproductio