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(2008)Journal ArticleBackground and Purpose: Anticoagulation reduces the risk of stroke in nonvalvular atrial fibrillation yet remains underused. We explored barriers to the use of anticoagulants among Australian family physicians. Methods: The authors conducted a representative, national survey. Results: Of the 596 (64.4%) eligible family physicians who participated, 15.8% reported having a patient with nonvalvular atrial fibrillation experience an intracranial hemorrhage with anticoagulation and 45.8% had a patient with known nonvalvular atrial fibrillation experience a stroke without anticoagulation. When presented with a patient at `very high risk` of stroke, only 45.6% of family physicians selected warfarin in the presence of a minor falls risk and 17.1% would anticoagulate if the patient had a treated peptic ulcer. Family physicians with less decisional conflict and longer-standing practices were more likely to endorse anticoagulation. Conclusion: Strategies to optimize the management of nonvalvular atrial fibrillation should address psychological barriers to using anticoagulation.
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(2006)Journal ArticleBackground and Purpose: Anticoagulation reduces the risk of stroke in nonvalvular atrial fibrillation yet remains underused. We explored barriers to the use of anticoagulants among Australian family physicians. Methods: The authors conducted a representative, national survey. Results: Of the 596 (64.4%) eligible family physicians who participated, 15.8% reported having a patient with nonvalvular atrial fibrillation experience an intracranial hemorrhage with anticoagulation and 45.8% had a patient with known nonvalvular atrial fibrillation experience a stroke without anticoagulation. When presented with a patient at "very high risk" of stroke, only 45.6% of family physicians selected warfarin in the presence of a minor falls risk and 17.1% would anticoagulate if the patient had a treated peptic ulcer. Family physicians with less decisional conflict and longer-standing practices were more likely to endorse anticoagulation. Conclusion: Strategies to optimize the management of nonvalvular atrial fibrillation should address psychological barriers to using anticoagulation.
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(2007)Working PaperThe Wald statistic is known to vary under reparameterization. This raises the question: which parameterization should be chosen, in order to optimize power of the Wald statistic? We specifically consider k-sample tests of generalized linear models and generalized estimating equations in which the alternative hypothesis contains only two parameters. Amongst a general class of parameterizations, we find the parameterization that maximizes power via analysis of the non-centrality parameter, and show how the effect on power of reparameterization depends on sampling design and the differences in variance across samples. There is no single parameterization with optimal power across all alternatives. The Wald statistic commonly used, that under the canonical parameterization, is optimal in some instances but it performs very poorly in others. We demonstrate results by example and by simulation, and describe their implications for likelihood ratio statistics and score statistics. We conclude that due to poor power properties, the routine use of score statistics and Wald statistics under the canonical parameterization for generalized estimating equations is a questionable practice.
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(1999)Conference Paper
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(2012)Journal ArticleSince the 1991 enactment of mandatory helmet legislation (MHL) for cyclists in New South Wales (NSW), Australia, there has been extensive debate as to its effect on head injury rates at a population level. Many previous studies have focused on the impact of MHL around the time of enactment, while little has been done to examine the ongoing effects. We aimed to extend prior work by investigating long-term trends in cyclist head and arm injuries over the period 1991–2010. The counts of cyclists hospitalised with head or arm injuries were jointly modelled with log-linear regression. The simultaneous modelling of related injury mechanisms avoids the need for actual exposure data and accounts for the effects of changes in the cycling environment, cycling behaviour and general safety improvements. Models were run separately with population counts, bicycle imports, the average weekday counts of cyclists in Sydney CBD and cycling estimates from survey data as proxy exposures. Overall, arm injuries were higher than head injuries throughout the study period, consistent with previous post-MHL observations. The trends in the two injury groups also significantly diverged, such that the gap between rates increased with time. The results suggest that the initial observed benefit of MHL has been maintained over the ensuing decades. There is a notable additional safety benefit after 2006 that is associated with an increase in cycling infrastructure spending. This implies that the effect of MHL is ongoing and progress in cycling safety in NSW has and will continue to benefit from focusing on broader issues such as increasing cycling infrastructure.
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(2013)Journal ArticleThis article responds to criticisms made in a rejoinder (Accident Analysis and Prevention 2012, 45: 107–109) questioning the validity of a study on the impact of mandatory helmet legislation (MHL) for cyclists in New South Wales, Australia. We systematically address the criticisms through clarification of our methods, extension of the original analysis and discussion of new evidence on the population-level effects of MHL. Extensions of our analysis confirm the original conclusions that MHL had a beneficial effect on head injury rates over and above background trends and changes in cycling participation. The ongoing debate around MHL draws attention away from important ways in which both safety and participation can be improved through investment in well-connected cycling infrastructure, fostering consideration between road users, and adequate legal protection for vulnerable road users. These are the essential elements for providing a cycling environment that encourages participation, with all its health, economic and environmental benefits, while maximising safety.
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(2010)Journal ArticleAlthough the normal probability distribution is the cornerstone of applying statistical methodology; data do not always meet the necessary normal distribution assumptions. In these cases, researchers often transform non normal data to a distribution that is approximately normal. Power transformations constitute a family of transformations, which include logarithmic and fractional exponent transforms. The Box-Cox method offers a simple method for choosing the most appropriate power transformation. Another option for data that is positively skewed, often used when measuring reaction times, is the Ex-Gaussian distribution which is a combination of the exponential and normal distributions. In this paper, the Box-Cox power transformation and Ex-Gaussian distribution will be discussed and compared in the context of positively skewed data. This discussion will demonstrate that the Box-Cox power transformation is simpler to apply and easier to interpret than the Ex-Gaussian distribution.
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(2007)Journal ArticleRecent new methods in Bayesian simulation have provided ways of evaluating posterior distributions in the presence of analytically or computationally intractable likelihood functions. Despite representing a substantial methodological advance, existing methods based on rejection sampling or Markov chain Monte Carlo can be highly inefficient and accordingly require far more iterations than may be practical to implement. Here we propose a sequential Monte Carlo sampler that convincingly overcomes these inefficiencies. We demonstrate its implementation through an epidemiological study of the transmission rate of tuberculosis.
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(2006)Journal ArticleTuberculosis can be studied at the population level by genotyping strains of Mycobacterium tuberculosis isolated from patients. We use an approximate Bayesian computational method in combination with a stochastic model of tuberculosis transmission and mutation of a molecular marker to estimate the net transmission rate, the doubling time, and the reproductive value of the pathogen. This method is applied to a published data set from San Francisco of tuberculosis genotypes based on the marker IS6110. The mutation rate of this marker has previously been studied, and we use those estimates to form a prior distribution of mutation rates in the inference procedure. The posterior point estimates of the key parameters of interest for these data are as follows: net transmission rate, 0.69/year [95% credibility interval (C.I.) 0.38, 1.08]; doubling time, 1.08 years (95% C.I. 0.64, 1.82); and reproductive value 3.4 (95% C.I. 1.4, 79.7). These figures suggest a rapidly spreading epidemic, consistent with observations of the resurgence of tuberculosis in the United States in the 1980s and 1990s.
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(1997)Other ResourceAudio-taped interview