Description: Glacial ogives are transverse topographic, wave-like surface features that form below icefalls on some alpine glaciers. Ground-penetrating radar surveys from the Gorner glacier system in the Swiss Alps reveal an along-flow periodicity in scattering intensity that correlates with ogives. The scattering appears in the ablation zone and occurs at 5–20 m depth. The geometry of the scattering mimics that of the ogives, although exaggerated in amplitude. We interpret the scattering to represent lateral variations in water content. We propose that as glacial ice accelerated and stretched through the icefall, seasonal fluctuations occurred in water infiltration to crevasses during the summer and subsequent freezing of that water in the crevasses in the winter. This seasonally varying infilling and freezing locally altered the distribution of temperature, creating zones of temperate ice with water inclusions that preferentially scatter radar energy. In addition to the scattering pattern, highly reflective planar features associated with these periodic regions of temperate ice are interpreted as water-filled fractures. A three-dimensional rendering of the orientation of these planar features precludes a "fold-and-thrust" hypothesis for the formation of the ogives.

Description: Objective To assess the adequacy of reporting of non-inferiority trials alongside the consistency and utility of current recommended analyses and guidelines. Design Review of randomised clinical trials that used a non-inferiority design published between January 2010 and May 2015 in medical journals that had an impact factor 〉10 ( JAMA Internal Medicine , Archives Internal Medicine , PLOS Medicine , Annals of Internal Medicine , BMJ , JAMA , Lancet and New England Journal of Medicine ). Data sources Ovid (MEDLINE). Methods We searched for non-inferiority trials and assessed the following: choice of non-inferiority margin and justification of margin; power and significance level for sample size; patient population used and how this was defined; any missing data methods used and assumptions declared and any sensitivity analyses used. Results A total of 168 trial publications were included. Most trials concluded non-inferiority (132; 79%). The non-inferiority margin was reported for 98% (164), but less than half reported any justification for the margin (77; 46%). While most chose two different analyses (91; 54%) the most common being intention-to-treat (ITT) or modified ITT and per-protocol, a large number of articles only chose to conduct and report one analysis (65; 39%), most commonly the ITT analysis. There was lack of clarity or inconsistency between the type I error rate and corresponding CIs for 73 (43%) articles. Missing data were rarely considered with (99; 59%) not declaring whether imputation techniques were used. Conclusions Reporting and conduct of non-inferiority trials is inconsistent and does not follow the recommendations in available statistical guidelines, which are not wholly consistent themselves. Authors should clearly describe the methods used and provide clear descriptions of and justifications for their design and primary analysis. Failure to do this risks misleading conclusions being drawn, with consequent effects on clinical practice.

Description: Objectives To investigate the extent to which cluster sizes vary in stepped-wedge cluster randomised trials (SW-CRT) and whether any variability is accounted for during the sample size calculation and analysis of these trials. Setting Any, not limited to healthcare settings. Participants Any taking part in an SW-CRT published up to March 2016. Primary and secondary outcome measures The primary outcome is the variability in cluster sizes, measured by the coefficient of variation (CV) in cluster size. Secondary outcomes include the difference between the cluster sizes assumed during the sample size calculation and those observed during the trial, any reported variability in cluster sizes and whether the methods of sample size calculation and methods of analysis accounted for any variability in cluster sizes. Results Of the 101 included SW-CRTs, 48% mentioned that the included clusters were known to vary in size, yet only 13% of these accounted for this during the calculation of the sample size. However, 69% of the trials did use a method of analysis appropriate for when clusters vary in size. Full trial reports were available for 53 trials. The CV was calculated for 23 of these: the median CV was 0.41 (IQR: 0.22–0.52). Actual cluster sizes could be compared with those assumed during the sample size calculation for 14 (26%) of the trial reports; the cluster sizes were between 29% and 480% of that which had been assumed. Conclusions Cluster sizes often vary in SW-CRTs. Reporting of SW-CRTs also remains suboptimal. The effect of unequal cluster sizes on the statistical power of SW-CRTs needs further exploration and methods appropriate to studies with unequal cluster sizes need to be employed.