Correcting for bias when estimating the cost of hospital-acquired infection : an analysis of lower respiratory tract infections in non-surgical patients

Hospital acquired infections (HAI) are costly but many are avoidable. Evaluating prevention programmes requires data on their costs and benefits. Estimating the actual costs of HAI (a measure of the cost savings due to prevention) is difficult as HAI changes cost by extending patient length of stay, yet, length of stay is a major risk factor for HAI. This endogeneity bias can confound attempts to measure accurately the cost of HAI. We propose a two-stage instrumental variables estimation strategy that explicitly controls for the endogeneity between risk of HAI and length of stay. We find that a 10% reduction in ex ante risk of HAI results in an expected savings of £693 ($US 984).

Error, Bias, and Long-Branch Attraction in Data for Two Chloroplast Photosystem Genes in Seed Plants

Sequences of two chloroplast photosystem genes, psaA and psbB, together comprising about 3,500 bp, were obtained for all five major groups of extant seed plants and several outgroups among other vascular plants. Strongly supported, but significantly conflicting, phylogenetic signals were obtained in parsimony analyses from partitions of the data into first and second codon positions versus third positions. In the former, both genes agreed on a monophyletic gymnosperms, with Gnetales closely related to certain conifers. In the latter, Gnetales are inferred to be the sister group of all other seed plants, with gymnosperms paraphyletic. None of the data supported the modern ‘‘anthophyte hypothesis,’’ which places Gnetales as the sister group of flowering plants. A series of simulation studies were undertaken to examine the error rate for parsimony inference. Three kinds of errors were examined: random error, systematic bias (both properties of finite data sets), and statistical inconsistency owing to long-branch attraction (an asymptotic property). Parsimony reconstructions were extremely biased for third-position data for psbB. Regardless of the true underlying tree, a tree in which Gnetales are sister to all other seed plants was likely to be reconstructed for these data. None of the combinations of genes or partitions permits the anthophyte tree to be reconstructed with high probability. Simulations of progressively larger data sets indicate the existence of long-branch attraction (statistical inconsistency) for third-position psbB data if either the anthophyte tree or the gymnosperm tree is correct. This is also true for the anthophyte tree using either psaA third positions or psbB first and second positions. A factor contributing to bias and inconsistency is extremely short branches at the base of the seed plant radiation, coupled with extremely high rates in Gnetales and nonseed plant outgroups. M. J. Sanderson,* M. F. Wojciechowski,*† J.-M. Hu,* T. Sher Khan,* and S. G. Brady

Exploring non-cancer pain conditions in a community sample : critiquing a current conceptual model of the acute to chronic pain transition and examining predictors of chronicity

This program of research examines the experience of chronic pain in a community sample. While, it is clear that like patient samples, chronic pain in non-patient samples is also associated with psychological distress and physical disability, the experience of pain across the total spectrum of pain conditions (including acute and episodic pain conditions) and during the early course of chronic pain is less clear. Information about these aspects of the pain experience is important because effective early intervention for chronic pain relies on identification of people who are likely to progress to chronicity post-injury. A conceptual model of the transition from acute to chronic pain was proposed by Gatchel (1991a). In brief, Gatchel’s model describes three stages that individuals who have a serious pain experience move through, each with worsening psychological dysfunction and physical disability. The aims of this program of research were to describe the experience of pain in a community sample in order to obtain pain-specific data on the problem of pain in Queensland, and to explore the usefulness of Gatchel’s Model in a non-clinical sample. Additionally, five risk factors and six protective factors were proposed as possible extensions to Gatchel’s Model. To address these aims, a prospective longitudinal mixed-method research design was used. Quantitative data was collected in Phase 1 via a comprehensive postal questionnaire. Phase 2 consisted of a follow-up questionnaire 3 months post-baseline. Phase 3 consisted of semi-structured interviews with a subset of the original sample 12 months post follow-up, which used qualitative data to provide a further in-depth examination of the experience and process of chronic pain from respondents’ point of view. The results indicate chronic pain is associated with high levels of anxiety and depressive symptoms. However, the levels of disability reported by this Queensland sample were generally lower than those reported by clinical samples and consistent with disability data reported in a New South Wales population-based study. With regard to the second aim of this program of research, while some elements of the pain experience of this sample were consistent with that described by Gatchel’s Model, overall the model was not a good fit with the experience of this non-clinical sample. The findings indicate that passive coping strategies (minimising activity), catastrophising, self efficacy, optimism, social support, active strategies (use of distraction) and the belief that emotions affect pain may be important to consider in understanding the processes that underlie the transition to and continuation of chronic pain.

Attention and memory bias for body image and health related information using an Emotional Stroop task in a non-clinical sample

It has been proposed that body image disturbance is a form of cognitive bias wherein schemas for self-relevant information guide the selective processing of appearancerelated information in the environment. This threatening information receives disproportionately more attention and memory, as measured by an Emotional Stroop and incidental recall task. The aim of this thesis was to expand the literature on cognitive processing biases in non-clinical males and females by incorporating a number of significant methodological refinements. To achieve this aim, three phases of research were conducted. The initial two phases of research provided preliminary data to inform the development of the main study. Phase One was a qualitative exploration of body image concerns amongst males and females recruited through the general community and from a university. Seventeen participants (eight male; nine female) provided information on their body image and what factors they saw as positively and negatively impacting on their self evaluations. The importance of self esteem, mood, health and fitness, and recognition of the social ideal were identified as key themes. These themes were incorporated as psycho-social measures and Stroop word stimuli in subsequent phases of the research. Phase Two involved the selection and testing of stimuli to be used in the Emotional Stroop task. Six experimental categories of words were developed that reflected a broad range of health and body image concerns for males and females. These categories were high and low calorie food words, positive and negative appearance words, negative emotion words, and physical activity words. Phase Three addressed the central aim of the project by examining cognitive biases for body image information in empirically defined sub-groups. A National sample of males (N = 55) and females (N = 144), recruited from the general community and universities, completed an Emotional Stroop task, incidental memory test, and a collection of psycho-social questionnaires. Sub-groups of body image disturbance were sought using a cluster analysis, which identified three sub-groups in males (Normal, Dissatisfied, and Athletic) and four sub-groups in females (Normal, Health Conscious, Dissatisfied, and Symptomatic). No differences were noted between the groups in selective attention, although time taken to colour name the words was associated with some of the psycho-social variables. Memory biases found across the whole sample for negative emotion, low calorie food, and negative appearance words were interpreted as reflecting the current focus on health and stigma against being unattractive. Collectively these results have expanded our understanding of processing biases in the general community by demonstrating that the processing biases are found within non-clinical samples and that not all processing biases are associated with negative functionality

Prevalence and correlates of low back pain among occupational therapy students in Northern Queensland

Background: Although low back pain (LBP) is an important issue for the health profession, few studies have examined LBP among occupational therapy students. Purpose. To investigate the prevalence and distribution of LBP, its adverse sequelae; and to identify potential risk factors.----------- Methods: In 2005, a self-reported questionnaire was administered to occupational therapy students in Northern Queensland.----------- Findings: The 12-month period-prevalence of LBP was 64.6%. Nearly half (46.9%) had experienced pain for over 2 days, 38.8% suffered LBP that affected their daily lives, and 24.5% had sought medical treatment. The prevalence of LBP ranged from 45.5 to 77.1% (p=0.004), while the prevalence of LBP symptoms persisting longer than two days was 34.1 to 62.5% (p=0.020). Logistic regression analysis indicated that year of study and weekly computer usage were statistically-significant LBP risk factors.----------- Implications: The occupational therapy profession will need to further investigate the high prevalence of student LBP identified in this study.

CPR training in households of patients with chest pain

The objectives of this study are to (1) quantify prior cardiopulmonary resuscitation (CPR) training in households of patients presenting to the Emergency Department (ED) with or without chest pain or ischaemic heart disease (IHD); (2) evaluate the willingness of household members to undertake CPR training; and (3) identify potential barriers to the learning and provision of bystander CPR. A cross-sectional study was conducted by surveying patients presenting to the ED of a metropolitan teaching hospital over a 6-month period. Two in five households of patients presenting with chest pain or IHD had prior training in CPR. This was no higher than for households of patients presenting without chest pain or IHD. Just under two in three households of patients presenting with chest pain or IHD were willing to participate in future CPR classes. Potential barriers to learning CPR included lack of information on CPR classes, perceived lack of intellectual and/or physical capability to learn CPR and concern about causing anxiety in the person at risk of cardiac arrest. Potential barriers to CPR provision included an unknown cardiac arrest victim and fear of infection. The ED provides an opportunity for increasing family and community capacity for bystander intervention through referral to appropriate training.

The impact of pain on the quality of life of people with multiple sclerosis: A community survey

The purpose of this study was to examine the impact of pain on functioning across multiple quality of life (QOL) domains among individuals with multiple sclerosis (MS). A total of 219 people were recruited from a regional MS society membership database to serve as the community-based study sample. All participants completed a questionnaire containing items about their demographic and clinical characteristics, validated measures of QOL and MS-related disability, and a question on whether or not they had experienced clinically significant pain in the preceding 2 weeks. Respondents who reported pain then completed an in-person structured pain interview assessing pain characteristics (intensity, quality, location, extent, and duration). Comparisons between participants with and without MS-related pain demonstrated that pain prevalence and intensity were strongly correlated with QOL: physical health, psychological health, level of independence, and global QOL were more likely to be impaired among people with MS when pain was present, and the extent of impairment was associated with the intensity of pain. Moreover, these relationships remained significant even after statistically controlling for multiple demographic and clinical covariates associated with self-reported QOL. These findings suggest that for people with MS, pain is an important source of distress and disability beyond that caused by neurologic impairments.

The efficacy of an augmented virtual reality system to alleviate pain in children undergoing burns dressing changes : a randomised controlled trial

In children, the pain and anxiety associated with acute burn dressing changes can be severe, with drug treatment alone frequently proving to be inadequate. Virtual reality (VR) systems have been successfully trialled in limited numbers of adult and paediatric burn patients. Augmented reality (AR) differs from VR in that it overlays virtual images onto the physical world, instead of creating a complete virtual world. This prospective randomised controlled trial investigated the use of AR as an adjunct to analgesia and sedation in children with acute burns. Forty-two children (30 male and 12 female), with an age range of 3–14 years (median age 9 years) and a total burn surface area ranging from 1 to 16% were randomised into a treatment (AR) arm and a control (basic cognitive therapy) arm after administration of analgesia and/or sedation. Pain scores, pulse rates (PR), respiratory rates (RR) and oxygen saturations (SaO2) were recorded pre-procedurally, at 10 min intervals and post-procedurally. Parents were also asked to grade their child's overall pain score for the dressing change. Mean pain scores were significantly lower (p = 0.0060) in the AR group compared to the control group, as were parental pain assessment scores (p = 0.015). Respiratory and pulse rates showed significant changes over time within groups, however, these were not significantly different between the two study groups. Oxygen saturation did not differ significantly over time or between the two study groups. This trial shows that augmented reality is a useful adjunct to pharmacological analgesia.

Addressing issues in sparseness, ecological bias and formulation of the adjacency matrix in Bayesian spatio-temporal analysis of disease counts

The main objective of this PhD was to further develop Bayesian spatio-temporal models (specifically the Conditional Autoregressive (CAR) class of models), for the analysis of sparse disease outcomes such as birth defects. The motivation for the thesis arose from problems encountered when analyzing a large birth defect registry in New South Wales. The specific components and related research objectives of the thesis were developed from gaps in the literature on current formulations of the CAR model, and health service planning requirements. Data from a large probabilistically-linked database from 1990 to 2004, consisting of fields from two separate registries: the Birth Defect Registry (BDR) and Midwives Data Collection (MDC) were used in the analyses in this thesis. The main objective was split into smaller goals. The first goal was to determine how the specification of the neighbourhood weight matrix will affect the smoothing properties of the CAR model, and this is the focus of chapter 6. Secondly, I hoped to evaluate the usefulness of incorporating a zero-inflated Poisson (ZIP) component as well as a shared-component model in terms of modeling a sparse outcome, and this is carried out in chapter 7. The third goal was to identify optimal sampling and sample size schemes designed to select individual level data for a hybrid ecological spatial model, and this is done in chapter 8. Finally, I wanted to put together the earlier improvements to the CAR model, and along with demographic projections, provide forecasts for birth defects at the SLA level. Chapter 9 describes how this is done. For the first objective, I examined a series of neighbourhood weight matrices, and showed how smoothing the relative risk estimates according to similarity by an important covariate (i.e. maternal age) helped improve the model’s ability to recover the underlying risk, as compared to the traditional adjacency (specifically the Queen) method of applying weights. Next, to address the sparseness and excess zeros commonly encountered in the analysis of rare outcomes such as birth defects, I compared a few models, including an extension of the usual Poisson model to encompass excess zeros in the data. This was achieved via a mixture model, which also encompassed the shared component model to improve on the estimation of sparse counts through borrowing strength across a shared component (e.g. latent risk factor/s) with the referent outcome (caesarean section was used in this example). Using the Deviance Information Criteria (DIC), I showed how the proposed model performed better than the usual models, but only when both outcomes shared a strong spatial correlation. The next objective involved identifying the optimal sampling and sample size strategy for incorporating individual-level data with areal covariates in a hybrid study design. I performed extensive simulation studies, evaluating thirteen different sampling schemes along with variations in sample size. This was done in the context of an ecological regression model that incorporated spatial correlation in the outcomes, as well as accommodating both individual and areal measures of covariates. Using the Average Mean Squared Error (AMSE), I showed how a simple random sample of 20% of the SLAs, followed by selecting all cases in the SLAs chosen, along with an equal number of controls, provided the lowest AMSE. The final objective involved combining the improved spatio-temporal CAR model with population (i.e. women) forecasts, to provide 30-year annual estimates of birth defects at the Statistical Local Area (SLA) level in New South Wales, Australia. The projections were illustrated using sixteen different SLAs, representing the various areal measures of socio-economic status and remoteness. A sensitivity analysis of the assumptions used in the projection was also undertaken. By the end of the thesis, I will show how challenges in the spatial analysis of rare diseases such as birth defects can be addressed, by specifically formulating the neighbourhood weight matrix to smooth according to a key covariate (i.e. maternal age), incorporating a ZIP component to model excess zeros in outcomes and borrowing strength from a referent outcome (i.e. caesarean counts). An efficient strategy to sample individual-level data and sample size considerations for rare disease will also be presented. Finally, projections in birth defect categories at the SLA level will be made.