Every Monday our authors provide a round-up of some of the most recently published peer reviewed articles from the field. We don’t cover everything, or even what’s most important – just a few papers that have interested the author. Visit our Resources page for links to more journals or follow the HealthEconBot. If you’d like to write one of our weekly journal round-ups, get in touch.
Contest models highlight inherent inefficiencies of scientific funding competitions. PLoS Biology [PubMed] Published 2nd January 2019
If you work in research you will have no doubt thought to yourself at one point that you spend more time applying to do research than actually doing it. You can spend weeks working on (what you believe to be) a strong proposal only for it to fail against other strong bids. That time could have been spent collecting and analysing data. Indeed, the opportunity cost of writing extensive proposals can be very high. The question arises as to whether there is another method of allocating research funding that reduces this waste and inefficiency. This paper compares the proposal competition to a partial lottery. In this lottery system, proposals are short, and among those that meet some qualifying standard those that are funded are selected at random. This system has the benefit of not taking up too much time but has the cost of reducing the average scientific value of the winning proposals. The authors compare the two approaches using an economic model of contests, which takes into account factors like proposal strength, public benefits, benefits to the scientist like reputation and prestige, and scientific value. Ultimately they conclude that, when the number of awards is smaller than the number of proposals worthy of funding, the proposal competition is inescapably inefficient. It means that researchers have to invest heavily to get a good project funded, and even if it is good enough it may still not get funded. The stiffer the competition the more researchers have to work to win the award. And what little evidence there is suggests that the format of the application makes little difference to the amount of time spent by researchers on writing it. The lottery mechanism only requires the researcher to propose something that is good enough to get into the lottery. Far less time would therefore be devoted to writing it and more time spent on actual science. I’m all for it!
Preventability of early versus late hospital readmissions in a national cohort of general medicine patients. Annals of Internal Medicine [PubMed] Published 5th June 2018
Hospital quality is hard to judge. We’ve discussed on this blog before the pitfalls of using measures such as adjusted mortality differences for this purpose. Just because a hospital has higher than expected mortality does not mean those death could have been prevented with higher quality care. More thorough methods assess errors and preventable harm in care. Case note review studies have suggested as little as 5% of deaths might be preventable in England and Wales. Another paper we have covered previously suggests then that the predictive value of standardised mortality ratios for preventable deaths may be less than 10%.
Another commonly used metric is readmission rates. Poor care can mean patients have to return to the hospital. But again, the question remains as to how preventable these readmissions are. Indeed, there may also be substantial differences between those patients who are readmitted shortly after discharge and those for whom it may take a longer time. This article explores the preventability of early and late readmissions in ten hospitals in the US. It uses case note review and a number of reviewers to evaluate preventability. The headline figures are that 36% of early readmissions are considered preventable compared to 23% of late readmissions. Moreover, it was considered that the early readmissions were most likely to have been preventable at the hospital whereas for late readmissions, an outpatient clinic or the home would have had more impact. All in all, another paper which provides evidence to suggest crude, or even adjusted rates, are not good indicators of hospital quality.
This article stems from a broader programme of work from these authors on good “Bayesian workflow”. That is to say, if we’re taking a Bayesian approach to analysing data, what steps ought we to be taking to ensure our analyses are as robust and reliable as possible? I’ve been following this work for a while as this type of pragmatic advice is invaluable. I’ve often read empirical papers where the authors have chosen, say, a logistic regression model with covariates x, y, and z and reported the outcomes, but at no point ever justified why this particular model might be any good at all for these data or the research objective. The key steps of the workflow include, first, exploratory data analysis to help set up a model, and second, performing model checks before estimating model parameters. This latter step is important: one can generate data from a model and set of prior distributions, and if the data that this model generates looks nothing like what we would expect the real data to look like, then clearly the model is not very good. Following this, we should check whether our inference algorithm is doing its job, for example, are the MCMC chains converging? We can also conduct posterior predictive model checks. These have had their criticisms in the literature for using the same data to both estimate and check the model which could lead to the model generalising poorly to new data. Indeed in a recent paper of my own, posterior predictive checks showed poor fit of a model to my data and that a more complex alternative was better fitting. But other model fit statistics, which penalise numbers of parameters, led to the alternative conclusions. So the simpler model was preferred on the grounds that the more complex model was overfitting the data. So I would argue posterior predictive model checks are a sensible test to perform but must be interpreted carefully as one step among many. Finally, we can compare models using tools like cross-validation.
This article discusses the use of visualisation to aid in this workflow. They use the running example of building a model to estimate exposure to small particulate matter from air pollution across the world. Plots are produced for each of the steps and show just how bad some models can be and how we can refine our model step by step to arrive at a convincing analysis. I agree wholeheartedly with the authors when they write, “Visualization is probably the most important tool in an applied statistician’s toolbox and is an important complement to quantitative statistical procedures.”