Royal Holloway Research Online
We Crashed, Now What?
Get PDFWe present an in-depth analysis of the crash-recovery problem and propose a novel approach to recover from otherwise fatal operating system (OS) crashes. We show how an unconventional, but careful, OS design, aided by automatic compiler-based code instrumentation, offers a practical solution towards the survivability of the entire system. Current results are encouraging and show that our approach is able to recover even the most critical OS subsystems without exposing the failure to user applications or hampering the scalability of the system
The Effects of Risk Preferences in Mixed-Strategy Equilibria of 2*2 Games
Get PDFWe consider the effects of risk preferences in mixed-strategy equilibria of 2 * 2 games, provided such equilibria exist. We identify sufficient conditions under which the expected payoff in the mixed equilibrium increases or decreases with the degree of risk aversion. We find that (at least moderate degrees of) risk aversion will frequently be beneficial in mixed equilibria
Defeating Network Node Subversion on SCADA Systems Using Probabilistic Packet Observation
Get PDFSupervisory control and data acquisition (SCADA) systems form a vital part of the critical infrastructure. Such systems have been subject to sophisticated and persistent attacks which are executed by processes under adversary supervision. Such attacks may be detected using inconsistencies in sensor readings or estimated behavior of the plant. However, to locate and eliminate malicious “agents” in networks, novel protocols are required to observe messaging behavior. In this paper, we propose a novel network protocol for SCADA systems which, for low computational cost, permits discovery and elimination of subverted nodes utilizing techniques related to probabilistic packet marking. We discuss its advantages over earlier work in this area, calculate message complexity requirements for detection and outline its resilience to various attack strategies
Methodological criteria for the assessment of moderators in systematic reviews of randomised controlled trials: a consensus study
Get PDFBackground
Current methodological guidelines provide advice about the assessment of sub-group analysis within RCTs, but do not specify explicit criteria for assessment. Our objective was to provide researchers with a set of criteria that will facilitate the grading of evidence for moderators, in systematic reviews.
Method
We developed a set of criteria from methodological manuscripts (n = 18) using snowballing technique, and electronic database searches. Criteria were reviewed by an international Delphi panel (n = 21), comprising authors who have published methodological papers in this area, and researchers who have been active in the study of sub-group analysis in RCTs. We used the Research ANd Development/University of California Los Angeles appropriateness method to assess consensus on the quantitative data. Free responses were coded for consensus and disagreement. In a subsequent round additional criteria were extracted from the Cochrane Reviewers' Handbook, and the process was repeated.
Results
The recommendations are that meta-analysts report both confirmatory and exploratory findings for sub-groups analysis. Confirmatory findings must only come from studies in which a specific theory/evidence based a-priori statement is made. Exploratory findings may be used to inform future/subsequent trials. However, for inclusion in the meta-analysis of moderators, the following additional criteria should be applied to each study: Baseline factors should be measured prior to randomisation, measurement of baseline factors should be of adequate reliability and validity, and a specific test of the interaction between baseline factors and interventions must be presented.
Conclusions
There is consensus from a group of 21 international experts that methodological criteria to assess moderators within systematic reviews of RCTs is both timely and necessary. The consensus from the experts resulted in five criteria divided into two groups when synthesising evidence: confirmatory findings to support hypotheses about moderators and exploratory findings to inform future research. These recommendations are discussed in reference to previous recommendations for evaluating and reporting moderator studies
Psychometric properties of two measures of psychological well-being in adult growth hormone deficiency
Get PDFBackground: Psychometric properties of two measures of psychological well-being were evaluated for adults with growth hormone deficiency (GHD): the General Well-being Index, (GWBI) – British version of the Psychological General Well-being Index, and the 12-item Well-being Questionnaire (W-BQ12).
Methods: Reliability, structure and other aspects of validity were investigated in a cross-sectional study of 157 adults with treated or untreated GHD, and sensitivity to change in a randomised placebo-controlled study of three months' growth hormone (GH) withdrawal from 12 of 21 GH-treated adults.
Results:Very high completion rates were evidence that both questionnaires were acceptable to respondents. Factor analyses did not indicate the existence of useful GWBI subscales, but confirmed the validity of calculating a GWBI Total score. However, very high internal consistency reliability (Cronbach's alpha = 0.96, N = 152), probably indicated some item redundancy in the 22-item GWBI. On the other hand, factor analyses confirmed the validity of the three W-BQ12 subscales of Negative Well-being, Energy, and Positive Well-being, each having excellent internal reliability (alphas of 0.86, 0.86 and 0.88, respectively, N from 152 to 154). There was no sign of item redundancy in the highly acceptable Cronbach's alpha of 0.93 (N = 148) for the whole W-BQ12 scale. Whilst neither questionnaire found significant differences between GH-treated and non-GH-treated patients, there were correlations (for GH-treated patients) with duration of GH treatment for GWBI Total (r = -0.36, p = 0.001, N = 85), W-BQ12 Total (r = 0.35, p = 0.001, N = 88) and for all W-BQ12 subscales: thus the longer the duration of GH treatment (ranging from 0.5 to 10 years), the better the well-being. Both questionnaires found that men had significantly better overall well-being than women. The W-BQ12 was more sensitive to change than the GWBI in the GH-Withdrawal study. A significant between-group difference in change in W-BQ12 Energy scores was found [t(18) = 3.25, p = 0.004, 2-tailed]: patients withdrawn from GH had reduced energy at end-point. The GWBI found no significant change.
Conclusion: The W-BQ12 is recommended in preference to the GWBI to measure well-being in adult GHD: it is considerably shorter, has three useful subscales, and has greater sensitivity to change
Evaluation of two health status measures in adults with growth hormone deficiency
Get PDFObjective: To evaluate the psychometric properties of two health status measures for adults with growth hormone deficiency (GHD): Nottingham Health Profile (NHP) and Short Form Health Survey (SF-36).
Design: (1) A cross-sectional survey of adults with treated or untreated GHD, to assess reliability and validity of the questionnaires. (2) A randomised, placebo-controlled study of 3 months’ GH withdrawal from GH-treated adults, to assess the questionnaires’ sensitivity to change.
Patients: (1) Cross-sectional survey of 157 patients with severe GHD (peak GH
Measurements: The NHP and SF-36 were used once in the cross-sectional survey, but twice in the GH-withdrawal study, at baseline and end-point (after 3 months).
Results: (1) Cross-sectional survey. Both questionnaires had high internal consistency reliability with subscale Cronbach’s alphas of > 0.73 (NHP) and > 0.78 (SF 36). Calculation of a NHP Total score, occasionally reported in the literature, was shown to be inadvisable. Overall, patients with GHD were found to have significantly worse perceived functioning than the UK general population in SF 36 subscales of General Health, Pain, Social Functioning, Role-Emotional, Role-Physical, and Vitality. Whilst neither questionnaire found significant differences between GH-treated and non-GH-treated patients, there were correlations with duration of GH treatment (p
Conclusions: The SF-36 is a better measure than the NHP of health status of people with GHD, owing to its greater discriminatory power with ability to detect lesser degrees of disability. It also has superior sensitivity to some sub-group differences and superior sensitivity to change than the NHP. The SF-36 is highly acceptable to respondents, and has very good internal consistency reliability. The SF-36 is recommended to measure the health status of adults with GHD
