958 research outputs found
MANOVA modelling of a chiropractic longitudinal study using multiple imputation
No full textThe purpose of this report is to present the detailed statistical analysis of a randomised, placebo-controlled trial comparing two different treatment modalities to an intervention of no known benefit for people with acute or subacute thoracic spine pain.
The therapy arms consist of Spinal Manipulative Therapy (SMT) and Graston Technique (GT) and the placebo is a non-functional ultrasound. A placebo group was utilised because at present there are no proven treatments for non-specific thoracic pain. This trial is registered with the Australia and New Zealand Clinical Trials Registry. Ethics approval has been granted by Murdoch University Human Research and Ethics Committee, number 2007/274.
The aim of this three arm trial was to test the efficacy of SMT and GT as independent modalities compared to detuned ultrasound for the outcomes of pain and disability. The latter were measured using the Visual Analogue Scale (VAS) and a modified Oswestry Back Pain Disability Index. The study was conducted at the Murdoch University Chiropractic student clinic in Perth, Australia, and the protocol published in Crothers et al (2008).
In this report, Section 2 provides an initial exploratory analysis of the data, Section 3 outlines the statistical models used in the final analysis, Section 4 defines these models in mathematical terms, Section 5 discusses the management of missing values via multiple imputation and Section 6 presents the results of the statistical modelling and hypothesis tests. The clinical study will be published in full elsewhere
Fast identification of biological pathways associated with a quantitative trait using group lasso with overlaps.
No full textWhere causal SNPs (single nucleotide polymorphisms) tend to accumulate within biological pathways, the incorporation of prior pathways information into a statistical model is expected to increase the power to detect true associations in a genetic association study. Most existing pathways-based methods rely on marginal SNP statistics and do not fully exploit the dependence patterns among SNPs within pathways.We use a sparse regression model, with SNPs grouped into pathways, to identify causal pathways associated with a quantitative trait. Notable features of our "pathways group lasso with adaptive weights" (P-GLAW) algorithm include the incorporation of all pathways in a single regression model, an adaptive pathway weighting procedure that accounts for factors biasing pathway selection, and the use of a bootstrap sampling procedure for the ranking of important pathways. P-GLAW takes account of the presence of overlapping pathways and uses a novel combination of techniques to optimise model estimation, making it fast to run, even on whole genome datasets.In a comparison study with an alternative pathways method based on univariate SNP statistics, our method demonstrates high sensitivity and specificity for the detection of important pathways, showing the greatest relative gains in performance where marginal SNP effect sizes are small
Estimating excess hazard ratios and net survival when covariate data are missing: strategies for multiple imputation.
No full textBACKGROUND: Net survival is the survival probability we would observe if the disease under study were the only cause of death. When estimated from routinely collected population-based cancer registry data, this indicator is a key metric for cancer control. Unfortunately, such data typically contain a non-negligible proportion of missing values on important prognostic factors (eg, tumor stage). METHODS: We carried out an empirical study to compare the performance of complete records analysis and several multiple imputation strategies when net survival is estimated via a flexible parametric proportional hazards model that includes stage, a partially observed categorical covariate. Starting from fully observed cancer registry data, we induced missingness on stage under three scenarios. For each of these scenarios, we simulated 100 incomplete datasets and evaluated the performance of the different strategies. RESULTS: Ordinal logistic models are not suitable for the imputation of tumor stage. Complete records analysis may lead to grossly misleading estimates of net survival, even when the missing data mechanism is conditionally independent of survival time given the covariates and the bias on the excess hazard ratios estimates is negligible. CONCLUSIONS: As key covariates are unlikely missing completely at random, studies estimating net survival should not use complete records. When the missingness can be inferred from available data, appropriate multiple imputation should be performed. In the context of flexible parametric proportional hazards models with a partially observed stage covariate, a multinomial logistic imputation model for stage should be used and should include the Nelson-Aalen cumulative hazard estimate and the event indicator
The impact of reduced inflation estimates on real output and productivity growth
No full textDespite posting their strongest sustained performance in many years, recent measures of output and productivity growth have still fallen short of their 1960-73 averages. Could data-measurement problems affecting the pricing of some services account for the inability of these widely tracked U.S. growth indexes to match their earlier rates?Economic indicators ; Productivity ; Gross domestic product ; Economic development ; Statistics ; Inflation (Finance)
Turning on and turning off: A focus group study of the factors that affect women's sexual arousal
No full textThis is a post print version of the article. The official published version can be accessed from the link below.The aim of this study was to inform the development of a questionnaire to assess a woman's tendency to respond with sexual excitation/inhibition in different situations. Nine focus groups, involving 80 women (M age = 34.3 years; range, 18-84), were conducted. Women described a wide range of physical (genital and nongenital), cognitive/emotional, and behavioral cues to arousal. The relationship between sexual interest (desire) and sexual arousal was complex; sexual interest was reported as sometimes preceding arousal, but at other times following it. Many women did not clearly differentiate between arousal and interest. Qualitative data on the factors that women perceived as enhancers and inhibitors of sexual arousal are presented, with a focus on the following themes: feelings about one's body; concern about reputation; unwanted pregnancy/ contraception; feeling desired versus feeling used by a partner; feeling accepted by a partner; style of approach/initiation; and negative mood. The findings can help inform conceptualizations of sexual arousal in women.This research was funded (in part) by a grant from the Lilly Centre for Women‟s Health
Common variants at 6p21.1 are associated with large artery atherosclerotic stroke
No full textGenome-wide association studies (GWAS) have not consistently detected replicable genetic risk factors for ischemic stroke, potentially due to etiological heterogeneity of this trait. We performed GWAS of ischemic stroke and a major ischemic stroke subtype (large artery atherosclerosis, LAA) using 1,162 ischemic stroke cases (including 421 LAA cases) and 1,244 population controls from Australia. Evidence for a genetic influence on ischemic stroke risk was detected, but this influence was higher and more significant for the LAA subtype. We identified a new LAA susceptibility locus on chromosome 6p21.1 (rs556621: odds ratio (OR) = 1.62, P = 3.9 × 10 -8) and replicated this association in 1,715 LAA cases and 52,695 population controls from 10 independent population cohorts (meta-analysis replication OR = 1.15, P = 3.9 × 10 -4; discovery and replication combined OR = 1.21, P = 4.7 × 10 -8). This study identifies a genetic risk locus for LAA and shows how analyzing etiological subtypes may better identify genetic risk alleles for ischemic stroke
Temporal characterization of the requests to Wikipedia
No full textThis paper presents an empirical study about the temporal patterns
characterizing the requests submitted by users to Wikipedia.
The study is based on the analysis of the log lines registered by the
Wikimedia Foundation Squid servers after having sent the appropriate
content in response to users' requests. The
analysis has been conducted regarding the ten most visited editions of
Wikipedia and has involved more than 14,000 million log lines
corresponding to the traffic of the entire year 2009. The conducted methodology
has mainly consisted in the parsing and filtering
of users' requests according to the study directives. As a result, relevant information
fields have been finally stored in a database for persistence and further
characterization. In this way, we, first, assessed, whether the traffic to Wikipedia could serve
as a reliable estimator of the overall traffic to all the Wikimedia Foundation
projects. Our subsequent analysis of the temporal evolutions corresponding to
the different types of requests to Wikipedia revealed interesting differences
and similarities among them that can be related to the users' attention to the Encyclopedia.
In addition, we have performed separated characterizations of each Wikipedia edition
to compare their respective evolutions over time
Absorption of light in finite semiconductor nanowire arrays and the effect of missing nanowires
No full textFunding Information: Funding: This research was funded by the Academy of Finland Flagship Program, Photonics Research and Innovation (PREIN), decision number: 320167. Publisher Copyright: © 2021 by the author. Licensee MDPI, Basel, Switzerland.When modelling the absorption in semiconductor nanowire (NW) arrays for solar cell and photodetector applications, the array is typically assumed to be infinitely periodic such that a single unit cell suffices for the simulations. However, any actual array is of a finite extent and might also show varying types of localized defects such as missing or electrically non-contacted individual NWs. Here, we study InP NWs of 2000 nm in length and 180 nm in diameter, placed in a square array of 400 nm in period, giving a rather optimized absorption of sunlight. We show that the absorption in the center NW of a finite N x N array converges already at N = 5 close to the value found for the corresponding infinite array. Furthermore, we show that a missing NW causes an enhanced absorption in neighboring nanowires, which compensates for 77% of the absorption loss due to the missing NW. In other words, an electrically non-contacted NW, which absorbs light but cannot contribute to the external short-circuit current, is a four times worse defect than a missing NW.Peer reviewe
An exploration of the effects of group summative assessment marking on higher education students’ overall marks
No full textGroupwork and group summative assessment (GSA) are important learning, teaching and assessment methods used by many educational institutions, not just universities. The differences between the marks that HEI students were awarded for their own independent individual summative assessment (IISA) work and their GSA marks were explored.
The study topic presented itself while the author was contemplating studying for a first degree, when it became apparent that group working and group summative assessment was included in summative assessment methods used in the chosen programme.
Three data sources were from UK undergraduates and graduates, and one was from Australian PG students. Module marks data were collected from over 4000 HE students. They were divided into eighteen faculty/year data sets from four HEI sources.
A systematic difference was found between the distributions of GSA and IISA marks, supporting Lejk et al. (1999). Lower IISA ability students scored higher in GSA modules than in IISA modules. Higher IISA ability students scored lower in GSA modules.
In addition, the mean GSA mark was higher than the mean IISA mark. The standard deviation of the GSA marks was lower than the SD of the IISA marks. Both of these findings support Downie (2001). The relationship was found to vary between the data sets, modules, assessment items and especially between faculties.
The results and conclusions from this study will empower stakeholders, enabling them to be better informed in their choice of first-degree study programmes. They will also allow the use and impact of GSA to be more transparent and better understood, leading to further research and improvement in practice
Do UK based weight management programmes cause weight loss maintenance in adults? A systematic review
No full textThe aim of this dissertation was to examine whether UK based weight management programmes promote weight loss maintenance (follow up of 12 months to assess effectiveness of intervention in weight loss) in adults through the process of a systematic review. The World Health Organisation (WHO) has described obesity as a "global epidemic". Weight management comprises two phases; weight loss and weight loss maintenance. The latter phase is the true goal for obesity and the most difficult element of weight management to achieve. However much less is know about this as compared with the weight loss phase. There is little purpose in committing time and money to reducing obesity if the weight is regained. This is counter-productive and weight loss maintenance is essential to combat the obesity epidemic. Searches were made for relevant information from a variety of scientific online databases and journals,. Seven articles met the inclusion criteria and were analysed in the review. All studies incorporated a multi-component (diet, exercise, behaviur modification) intervention approach. All control and internvetion groups reported weight loss at 12 months when compared with baseline. All groups recieved an intervention. One study reported a significant difference (P<0.05) between groups. Four studies reported on at least one component (diet, physical activity, behaviour modification) however there was not enough information to conclude whether they complied with national guidelines (NICE CG43 and SIGN 115). High attrition rates and loss to follow up are problematic for each study except one. Analysis on an intention to treat basis was common however this is problematic and there are alternative methods which may be more suitable for dealing with missing data
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