Estimating principal plane positions for ocular power calculations in children and adults

2021 ◽  
Author(s):  
Jos J. Rozema
Keyword(s):  
Principal Plane ◽  
Power Calculations

Simulation-based power calculations for conjoint experiments

2020 ◽  
Author(s):  
Brett J. Gall
Keyword(s):  
Power Calculations ◽  
Simulation Based ◽  
Different Types ◽  
Power Analyses

I introduce code for each step required to conduct power analyses through simulation in R, with special attention to the challenges of conjoint experiments. We’ll slowly build up our code until we have something that fairly easily can simulate power of different types of conjoint experiments. The goal is provide enough detail and intuition to write up your own custom simulations.

scholarly journals Estimates of the mean difference in orthopaedic randomized trials: obligatory yet obscure

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Lauri Raittio ◽  
Antti Launonen ◽  
Ville M. Mattila ◽  
Aleksi Reito
Keyword(s):  
Primary Outcome ◽  
Outcome Measure ◽  
Patient Reported Outcome ◽  
Ceiling Effect ◽  
Mean Difference ◽  
Discussion Section ◽  
Power Calculations ◽  
Randomized Controlled ◽  
Patient Reported ◽  
The Mean

Abstract Background Randomized controlled trials in orthopaedics are powered to mainly find large effect sizes. A possible discrepancy between the estimated and the real mean difference is a challenge for statistical inference based on p-values. We explored the justifications of the mean difference estimates used in power calculations. The assessment of distribution of observations in the primary outcome and the possibility of ceiling effects were also assessed. Methods Systematic review of the randomized controlled trials with power calculations in eight clinical orthopaedic journals published between 2016 and 2019. Trials with one continuous primary outcome and 1:1 allocation were eligible. Rationales and references for the mean difference estimate were recorded from the Methods sections. The possibility of ceiling effect was addressed by the assessment of the weighted mean and standard deviation of the primary outcome and its elaboration in the Discussion section of each RCT where available. Results 264 trials were included in this study. Of these, 108 (41 %) trials provided some rationale or reference for the mean difference estimate. The most common rationales or references for the estimate of mean difference were minimal clinical important difference (16 %), observational studies on the same subject (8 %) and the ‘clinical relevance’ of the authors (6 %). In a third of the trials, the weighted mean plus 1 standard deviation of the primary outcome reached over the best value in the patient-reported outcome measure scale, indicating the possibility of ceiling effect in the outcome. Conclusions The chosen mean difference estimates in power calculations are rarely properly justified in orthopaedic trials. In general, trials with a patient-reported outcome measure as the primary outcome do not assess or report the possibility of the ceiling effect in the primary outcome or elaborate further in the Discussion section.

An Audit of Behcet’s Syndrome Research: A 10-year Survey

2010 ◽  
Vol 38 (1) ◽  
pp. 99-103 ◽  
Author(s):  
FEHIM ESEN ◽  
ELIZABETH K. SCHIMMEL ◽  
HASAN YAZICI ◽  
YUSUF YAZICI
Keyword(s):  
Disease Control ◽  
Demographic Data ◽  
Considerable Proportion ◽  
Behçet’S Syndrome ◽  
Control Groups ◽  
Power Calculations ◽  
Behçet's Syndrome ◽  
Behcet’S Syndrome ◽  
Prospective Longitudinal ◽  
Behcet's Syndrome

Objective.Data suggest that the use of disease control groups and proper use of power calculations were neglected in published reports. We surveyed these and other methodological shortcomings in reports published within the last decade about one specific topic, Behcet’s syndrome. We reason that recognizing such methodological shortcomings will lead to better quality clinical and basic science articles.Methods.Articles published in the 15 highest impact factor journals on rheumatology, ophthalmology, dermatology, and general medicine between January 1999 and January 2009 were searched for original reports on Behcet’s syndrome. Study designs (study types and time element), control groups, demographic data, use of power calculations, and reporting of negative results were specifically tabulated.Results.Most studies on Behcet’s syndrome were cross-sectional (83%). Prospective longitudinal studies were few (7%). In a considerable proportion of papers (21%), some basic demographic data were missing. Power calculations were rare (3%) even in randomized controlled trials and were not considered at all in clinical hypothesis-testing. Disease control groups were present in slightly over half of clinical and laboratory original research, while just 13% of genetic association studies included disease controls. Only 12% of all reports concerned mainly negative outcomes.Conclusion.A considerable number of the published research articles have methodological weaknesses. The generalizability of what we observed in Behcet’s syndrome to other research topics needs to be formally studied.

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