The MIDAS touch: accurate and scalable missing-data imputation with deep learning

Principled methods for analyzing missing values, based chiefly on multiple imputation, have become increasingly popular yet can struggle to handle the kinds of large and complex data that are also becoming common. We propose an accurate, fast, and scalable approach to multiple imputation, which we call MIDAS (Multiple Imputation with Denoising Autoencoders). MIDAS employs a class of unsupervised neural networks known as denoising autoencoders, which are designed to reduce dimensionality by corrupting and attempting to reconstruct a subset of data. We repurpose denoising autoencoders for multiple imputation by treating missing values as an additional portion of corrupted data and drawing imputations from a model trained to minimize the reconstruction error on the originally observed portion. Systematic tests on simulated as well as real social science data, together with an applied example involving a large-scale electoral survey, illustrate MIDAS’s accuracy and efficiency across a range of settings. We provide open-source software for implementing MIDAS

How multiple imputation makes a difference

Political scientists increasingly recognize that multiple imputation represents a superior strategy for analyzing missing data to the widely used method of listwise deletion. However, there has been little systematic investigation of how multiple imputation affects existing empirical knowledge in the discipline. This article presents the first large-scale examination of the empirical effects of substituting multiple imputation for listwise deletion in political science. The examination focuses on research in the major subfield of comparative and international political economy (CIPE) as an illustrative example. Specifically, I use multiple imputation to reanalyze the results of almost every quantitative CIPE study published during a recent five-year period in International Organization and World Politics, two of the leading subfield journals in CIPE. The outcome is striking: in almost half of the studies, key results “disappear” (by conventional statistical standards) when reanalyzed

Beyond institutional design: explaining the performance of international organizations

International organizations (IOs) have long been a central focus of scholarship in international relations, yet we know remarkably little about their performance. This article offers an explanation for differences in the performance of IOs and tests it using the first quantitative data set on the topic. I argue that the primary obstacle to effective institutional performance is not deviant behavior by IO officials—as conventional “rogue-agency” analyses suggest—but the propensity of states to use IOs to promote narrow national interests rather than broader organizational objectives. IOs that enjoy policy autonomy vis-à-vis states will thus exhibit higher levels of performance. However, in the international context policy autonomy cannot be guaranteed by institutional design. Instead, it is a function of (1) the existence of (certain types of) institutionalized alliances between IOs and actors above and below the state; and (2) the technical complexity of IO activities. I provide empirical evidence for the argument by constructing and analyzing a cross-sectional data set on IO performance—based in part on a new wave of official government evaluations of IOs and in part on an original survey of IO staff—and conducting a comparative case study in the realm of global food security

The missing dimension of the political resource curse debate

Given the methodological sophistication of the debate over the “political resource curse”—the purported negative relationship between natural resource wealth (in particular oil wealth) and democracy—it is surprising that scholars have not paid more attention to the basic statistical issue of how to deal with missing data. This article highlights the problems caused by the most common strategy for analyzing missing data in the political resource curse literature—listwise deletion—and investigates how addressing such problems through the best-practice technique of multiple imputation affects empirical results. I find that multiple imputation causes the results of a number of influential recent studies to converge on a key common finding: A political resource curse does exist, but only since the widespread nationalization of petroleum industries in the 1970s. This striking finding suggests that much of the controversy over the political resource curse has been caused by a neglect of missing-data issues

The application of ordinal regression models in quality of life scales used in gerontology

Aim of the Thesis: The area of health-related quality of life has received increasing attention particularly in gerontology. As this area grows in importance, issues such as the design and analysis of instruments that measure this multi-dimensional outcome need to be addressed. Ordinal regression models are statistical methods that can be used to analyse ordered health-related quality of life measures. However, their use is limited in the literature. The aims of this thesis are (i) to compute all ordinal regression models and compare these models with other statistical methods (such as linear regression and binary logistic regression models) and (ii) assess the use of the stereotype ordinal regression model. Procedure: The data used to implement the regression models was from the Medical Research Council Cognitive and Function Ageing Study (MRC CFAS). In particular, two measures were chosen: the Townsend Disability Scale and the Health Status question. Results: Linear regression models were found to summarise the ordinal data inadequately given both ordinal measures. Binary logistic regression models were only adequate for analysing ordinal quality of life scales, if one could assume that the odds ratios were the same over all the binary groupings of the ordinal scale. However, one may still encounter other problems related to multiple testing or different effects in different models. Ordinal regression models provide a more sensitive and comprehensive analysis. These methods are easily adapted to different types of ordinal quality of life data. The 'best-fit' ordinal regression model for the health status ordinal categories was the partially constrained adjacent category model. The 'best-fit' model for the Townsend Disability Scale was the fully constrained continuation ratio model. Conclusions: This study has provided a method (based on first principles) of implementing all ordinal regression models. The comprehensive results from this thesis, suggest that ordinal regression models are indeed superior compared to other methods for analysing ordinal quality of life data. Evidence suggested that the stereotype model was of little use. Key words: Gerontology, health-related quality of life, ordinal regression models

A national facilitation project to improve primary palliative care : impact of the Gold Standards Framework on process and self-ratings of quality

Background: Improving quality of end-of-life care is a key driver of UK policy. The Gold Standards Framework (GSF) for Palliative Care aims to strengthen primary palliative care through facilitating implementation of systematic clinical and organisational processes. Objectives: To describe the general practices that participated in the GSF programme in 2003–5 and the changes in process and perception of quality that occurred in the year following entry into the programme, and to identify factors associated with the extent of change. Methods: Participating practices completed a questionnaire at baseline and another approximately 12 months later. Data were derived from categorical questions about the implementation of 35 organisational and clinical processes, and self-rated assessments of quality, associated with palliative care provision. Participants: 1305 practices (total registered population almost 10 million). Follow-up questionnaire completed by 955 (73.2%) practices (after mean (SD) 12.8 (2.8) months; median 13 months). Findings: Mean increase in total number of processes implemented (maximum = 35) was 9.6 (95% CI 9.0 to 10.2; p<0.001; baseline: 15.7 (SD 6.4), follow-up: 25.2 (SD 5.2)). Extent of change was largest for practices with low baseline scores. Aspects of process related to coordination and communication showed the greatest change. All dimensions of quality improved following GSF implementation; change was highest for the "quality of palliative care for cancer patients" and "confidence in assessing, recording and addressing the physical and psychosocial areas of patient care". Conclusion: Implementation of the GSF seems to have resulted in substantial improvements in process and quality of palliative care. Further research is required of the extent to which this has enhanced care (physical, practical and psychological outcomes) for patients and carers

Group treatments for sensitive health care problems : a randomised controlled trial of group versus individual physiotherapy sessions for female urinary incontinence

Background: The aim was to compare effectiveness of group versus individual sessions of physiotherapy in terms of symptoms, quality of life, and costs, and to investigate the effect of patient preference on uptake and outcome of treatment. Methods: A pragmatic, multi-centre randomised controlled trial in five British National Health Service physiotherapy departments. 174 women with stress and/or urge incontinence were randomised to receive treatment from a physiotherapist delivered in a group or individual setting over three weekly sessions. Outcome were measured as Symptom Severity Index; Incontinence-related Quality of Life questionnaire; National Health Service costs, and out of pocket expenses. Results: The majority of women expressed no preference (55%) or preference for individual treatment (36%). Treatment attendance was good, with similar attendance with both service delivery models. Overall, there were no statistically significant differences in symptom severity or quality of life outcomes between the models. Over 85% of women reported a subjective benefit of treatment, with a slightly higher rating in the individual compared with the group setting. When all health care costs were considered, average cost per patient was lower for group sessions (Mean cost difference £52.91 95%, confidence interval (£25.82 - £80.00)). Conclusion: Indications are that whilst some women may have an initial preference for individual treatment, there are no substantial differences in the symptom, quality of life outcomes or non-attendance. Because of the significant difference in mean cost, group treatment is recommended

Is protocolised weaning that includes early extubation onto non-invasive ventilation more cost effective than protocolised weaning without non-invasive ventilation? Findings from the Breathe Study

Background Optimising techniques to wean patients from invasive mechanical ventilation (IMV) remains a key goal of intensive care practice. The use of non-invasive ventilation (NIV) as a weaning strategy (transitioning patients who are difficult to wean to early NIV) may reduce mortality, ventilator-associated pneumonia and intensive care unit (ICU) length of stay. Objectives Our objectives were to determine the cost effectiveness of protocolised weaning, including early extubation onto NIV, compared with weaning without NIV in a UK National Health Service setting. Methods We conducted an economic evaluation alongside a multicentre randomised controlled trial. Patients were randomised to either protocol-directed weaning from mechanical ventilation or ongoing IMV with daily spontaneous breathing trials. The primary efficacy outcome was time to liberation from ventilation. Bivariate regression of costs and quality-adjusted life-years (QALYs) provided estimates of the incremental cost per QALY and incremental net monetary benefit (INMB) overall and for subgroups [presence/absence of chronic obstructive pulmonary disease (COPD) and operative status]. Long-term cost effectiveness was determined through extrapolation of survival curves using flexible parametric modelling. Results NIV was associated with a mean INMB of £620 ($US885) (cost-effectiveness threshold of £20,000 per QALY) with a corresponding probability of 58$US6594 per QALY gained). Conclusions The probability of NIV being cost effective relative to weaning without NIV ranged between 57 and 59% overall and between 82 and 87% for the COPD subgroup

Does Structured Exercise Improve Cognitive Impairment in People with Mild to Moderate Dementia? A Cost-Effectiveness Analysis from a Confirmatory Randomised Controlled Trial:The Dementia and Physical Activity (DAPA) Trial

Background Previous studies suggest that physical exercise could slow dementia progression. However, evidence for the cost effectiveness of structured exercise is conflicting and based on small trials. Objectives The objective of this study was to compare the cost effectiveness of a tailored, structured, moderate- to high-intensity exercise programme versus usual care in people with mild to moderate dementia. Methods An economic evaluation was conducted from the UK National Health Service and personal social services perspective, based on data from a large randomised controlled trial. The primary clinical outcome was the participant reported ADAS-Cog (Alzheimer’s Disease Assessment Scale–Cognitive Subscale) at 12 months. Costs (£; 2014–2015 prices) were collected prospectively over a 12-month follow-up period. A bivariate regression of costs and quality-adjusted life-years (QALYs), with multiple imputation of missing data, was conducted with the view to estimating the incremental cost per QALY gained and the incremental net monetary benefit (INMB) associated with the exercise programme plus usual care versus usual care. Sensitivity analyses were undertaken to assess the impact of uncertainty surrounding aspects of the economic evaluation, and pre-specified subgroup analyses explored heterogeneity in the cost-effectiveness results. Results Participants (n = 494) were randomised to exercise plus usual care or usual care only. By 12 months the mean ADAS-Cog score had worsened slightly to 25.2 (standard deviation [SD] 12.3) in the exercise arm and 23.8 (SD 10.4) in the usual care: difference − 1.4, 95% confidence interval (CI) − 2.6 to − 0.2 (p = 0.03). The mean (standard error [SE]) costs over 12 months for experimental versus control was £5945 (USD7856) versus £4597 (USD6574), respectively; (difference: £1347 [$1926]; p = 0.0426). Mean (SE) QALY estimates were 0.787 (0.012) versus 0.826 (0.019), respectively (p = 0.090). The probability that the exercise programme is cost effective was  Conclusions Building on the clinical results of the trial, which showed that the structured exercise programme evaluated does not slow cognitive impairment in people with mild to moderate dementia, this economic evaluation shows that the programme is not cost effective.</p