Summarizing empirical information on between-study heterogeneity for Bayesian random-effects meta-analysis.

In Bayesian meta-analysis, the specification of prior probabilities for the between-study heterogeneity is commonly required, and is of particular benefit in situations where only few studies are included. Among the considerations in the set-up of such prior distributions, the consultation of available empirical data on a set of relevant past analyses sometimes plays a role. How exactly to summarize historical data sensibly is not immediately obvious; in particular, the investigation of an empirical collection of heterogeneity estimates will not target the actual problem and will usually only be of limited use. The commonly used normal-normal hierarchical model for random-effects meta-analysis is extended to infer a heterogeneity prior. Using an example data set, we demonstrate how to fit a distribution to empirically observed heterogeneity data from a set of meta-analyses. Considerations also include the choice of a parametric distribution family. Here, we focus on simple and readily applicable approaches to then translate these into (prior) probability distributions.

Assessment of prostate-specific antigen screening: an evidence-based report by the German Institute for Quality and Efficiency in Health Care.

CONTEXT: Prostate-specific antigen (PSA) testing increases prostate cancer diagnoses and reduces long-term disease-specific mortality, but also results in overdiagnoses and treatment-related harms. OBJECTIVE: To systematically assess the benefits and harms of population-based PSA screening and the potential net benefit to inform health policy decision-makers in Germany. EVIDENCE ACQUISITION: We performed a protocol-guided comprehensive literature search according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement. All steps were performed by one or two investigators; any discrepancies were resolved by consensus. To allow subgroup analyses for identifying the optimal screening parameters, the eight national trials conducted under the umbrella of the European Randomised study of Screening for Prostate Cancer (ERSPC) were included as individual trials. EVIDENCE SYNTHESIS: We included a total 11 randomised controlled trials (RCTs) with a total of 416 000 study participants. For all-cause mortality, we found neither benefit nor harm. PSA screening was associated with a reduced risk of both prostate cancer mortality and the development of metastases. For the outcomes of health-related quality of life, adverse effects and the consequences of false-negative screening results there was no difference; however, this was due to the lack of eligible RCT data. Finally, PSA screening was associated with large numbers of overdiagnoses with adverse downstream consequences of unnecessary treatment (e.g. incontinence, erectile dysfunction) and large numbers of false-positive PSA tests leading to biopsies associated with a small but not negligible risk of complications. Limitations of this assessment include the clinical heterogeneity and methodological limitations of the underlying studies. CONCLUSIONS: The benefits of PSA-based prostate cancer screening do not outweigh its harms. We failed to identify eligible screening studies of newer biomarkers, PSA derivatives or modern imaging modalities, which may alter the balance of benefit to harm. PATIENT SUMMARY: In the present study, we reviewed the evidence on the PSA blood test to screen men without symptoms for prostate cancer. We found that the small benefits experienced by some men do not outweigh the harms to many more men.

A simulation study to compare different estimation approaches for network meta-analysis and corresponding methods to evaluate the consistency assumption.

BACKGROUND: Network meta-analysis (NMA) is becoming increasingly popular in systematic reviews and health technology assessments. However, there is still ambiguity concerning the properties of the estimation approaches as well as for the methods to evaluate the consistency assumption. METHODS: We conducted a simulation study for networks with up to 5 interventions. We investigated the properties of different methods and give recommendations for practical application. We evaluated the performance of 3 different models for complex networks as well as corresponding global methods to evaluate the consistency assumption. The models are the frequentist graph-theoretical approach netmeta, the Bayesian mixed treatment comparisons (MTC) consistency model, and the MTC consistency model with stepwise removal of studies contributing to inconsistency identified in a leverage plot. RESULTS: We found that with a high degree of inconsistency none of the evaluated effect estimators produced reliable results, whereas with moderate or no inconsistency the estimator from the MTC consistency model and the netmeta estimator showed acceptable properties. We also saw a dependency on the amount of heterogeneity. Concerning the evaluated methods to evaluate the consistency assumption, none was shown to be suitable. CONCLUSIONS: Based on our results we recommend a pragmatic approach for practical application in NMA. The estimator from the netmeta approach or the estimator from the Bayesian MTC consistency model should be preferred. Since none of the methods to evaluate the consistency assumption showed satisfactory results, users should have a strong focus on the similarity as well as the homogeneity assumption.

Comparison of Bayesian methods for flexible modeling of spatial risk surfaces in disease mapping.

Bayesian hierarchical models usually model the risk surface on the same arbitrary geographical units for all data sources. Poisson/gamma random field models overcome this restriction as the underlying risk surface can be specified independently to the resolution of the data. Moreover, covariates may be considered as either excess or relative risk factors. We compare the performance of the Poisson/gamma random field model to the Markov random field (MRF)-based ecologic regression model and the Bayesian Detection of Clusters and Discontinuities (BDCD) model, in both a simulation study and a real data example. We find the BDCD model to have advantages in situations dominated by abruptly changing risk while the Poisson/gamma random field model convinces by its flexibility in the estimation of random field structures and by its flexibility incorporating covariates. The MRF-based ecologic regression model is inferior. WinBUGS code for Poisson/gamma random field models is provided.

Bayesian random-effects meta-analysis with empirical heterogeneity priors for application in health technology assessment with very few studies.

In Bayesian random-effects meta-analysis, the use of weakly informative prior distributions is of particular benefit in cases where only a few studies are included, a situation often encountered in health technology assessment (HTA). Suggestions for empirical prior distributions are available in the literature but it is unknown whether these are adequate in the context of HTA. Therefore, a database of all relevant meta-analyses conducted by the Institute for Quality and Efficiency in Health Care (IQWiG, Germany) was constructed to derive empirical prior distributions for the heterogeneity parameter suitable for HTA. Previously, an extension to the normal-normal hierarchical model had been suggested for this purpose. For different effect measures, this extended model was applied on the database to conservatively derive a prior distribution for the heterogeneity parameter. Comparison of a Bayesian approach using the derived priors with IQWiG's current standard approach for evidence synthesis shows favorable properties. Therefore, these prior distributions are recommended for future meta-analyses in HTA settings and could be embedded into the IQWiG evidence synthesis approach in the case of very few studies.

Single-fraction stereotactic radiosurgery versus microsurgical resection for the treatment of vestibular schwannoma: a systematic review and meta-analysis.

BACKGROUND: Vestibular schwannomas are benign tumours for which various treatments are available. We performed a systematic review of prospective controlled trials comparing the patient-relevant benefits and harms of single-fraction stereotactic radiosurgery (sfSRS) with microsurgical resection (MR) in patients with vestibular schwannoma. METHODS: We searched for randomized controlled trials (RCTs) and non-randomized prospective controlled trials in MEDLINE, Embase, the Cochrane Central Register of Controlled Trials, and study registries (last search: 09/2021) and also screened reference lists of relevant systematic reviews. Manufacturers were asked to provide unpublished data. Eligible studies investigated at least one patient-relevant outcome. We assessed the risk of bias (high or low) at the study and outcome level. If feasible, meta-analyses were performed. We graded the results into different categories (hint, indication, or proof of greater benefit or harm). RESULTS: We identified three non-randomized prospective controlled trials of generally low quality with evaluable data on 339 patients with unilateral vestibular schwannoma. There was an indication of greater benefit of sfSRS compared with MR for facial palsy (OR 0.06, 95% CI 0.02-0.21, p < 0.001, 2 studies), hearing function (no pooled estimate available, 2 studies), and length of hospital stay (no pooled estimate available, 2 studies). We found no clinically relevant differences for mortality, vertigo, headaches, tinnitus, balance function, work disability, adverse events, and health-related quality of life. CONCLUSIONS: Our systematic review indicates that sfSRS has greater benefits than MR in patients with unilateral vestibular schwannoma. However, it is unclear whether this conclusion still holds after 2 years, as long-term studies are lacking. It is also unclear whether the effects of sfSRS are similar in patients with bilateral vestibular schwannomas. Long-term prospective studies including patients with this condition would therefore be useful. SYSTEMATIC REVIEW REGISTRATION: The full (German language) protocol and report (Commission No. N20-03) are available on the institute's website: www.iqwig.de/en/projects/n20-03.html.

On weakly informative prior distributions for the heterogeneity parameter in Bayesian random-effects meta-analysis.

The normal-normal hierarchical model (NNHM) constitutes a simple and widely used framework for meta-analysis. In the common case of only few studies contributing to the meta-analysis, standard approaches to inference tend to perform poorly, and Bayesian meta-analysis has been suggested as a potential solution. The Bayesian approach, however, requires the sensible specification of prior distributions. While noninformative priors are commonly used for the overall mean effect, the use of weakly informative priors has been suggested for the heterogeneity parameter, in particular in the setting of (very) few studies. To date, however, a consensus on how to generally specify a weakly informative heterogeneity prior is lacking. Here we investigate the problem more closely and provide some guidance on prior specification.

Ginkgo biloba in Alzheimer's disease: a systematic review.

This systematic review determines the benefit of treatment with Ginkgo biloba (Ginkgo) in Alzheimer's disease (AD) concerning patient-relevant outcomes. Bibliographic databases, clinical trial and study result registries were searched for randomized controlled trials (RCTs) in patients with AD (follow-up ≥16 weeks) comparing Ginkgo to placebo or a different treatment option. Manufacturers were asked to provide unpublished data. If feasible, data were pooled by meta-analysis. Six studies were eligible; overall, high heterogeneity was shown for most outcomes, except safety aspects. Among studies administering high-dose Ginkgo (240 mg), all studies favour treatment though effects remain heterogeneous. In this subgroup, a benefit of Ginkgo exists for activities of daily living. Cognition and accompanying psychopathological symptoms show an indication of a benefit. A harm of Ginkgo is not evident. An estimation of the effect size was not possible for any outcome. Further evidence is needed which focuses especially on subgroups of AD patients.

Trial registry searches for randomized controlled trials of new drugs required registry-specific adaptation to achieve adequate sensitivity.

OBJECTIVES: To analyze the availability of randomized controlled trials (RCTs) of new drugs in trial registries and to develop and test different search strategies in ClinicalTrials.gov (CT.gov), the EU Clinical Trials Register (EU-CTR), and the International Clinical Trials Registry Platform (ICTRP). STUDY DESIGN AND SETTING: Information from dossiers submitted by pharmaceutical companies was analyzed regarding the registration of the included RCTs in CT.gov, EU-CTR and ICTRP; different search strategies were developed and tested to determine performance. RESULTS: A total of 192 (95%) of 203 RCTs on newly approved drugs were registered in CT.gov; the 11 nonregistered trials were completed before 2005 or represented non-RCTs. Simple searches for RCTs on 18 new drugs using the generic drug name yielded a sensitivity of 94% in CT.gov (EU-CTR: 71%; ICTRP: 60%). The main reason for study nondetection was the sole use of the drug code in the registry entries. Simple searches for RCTs on 13 conditions using reasonably inferred search terms yielded a sensitivity of 100% in CT.gov. CONCLUSION: Almost all relevant RCTs on newly approved drugs will probably be identified in CT.gov alone. A sensitive search in CT.gov can be conducted using single search terms. The searches in ICTRP and EU-CTR should include several search terms (e.g., derived via text analysis).

Assumptions of Mixed Treatment Comparisons in Health Technology Assessments - Challenges and Possible Steps for Practical Application.

The validity of mixed treatment comparisons (MTCs), also called network meta-analysis, relies on whether it is reasonable to accept the underlying assumptions on similarity, homogeneity, and consistency. The aim of this paper is to propose a practicable approach to addressing the underlying assumptions of MTCs. Using data from clinical studies of antidepressants included in a health technology assessment (HTA), we present a stepwise approach to dealing with challenges related to checking the above assumptions and to judging the robustness of the results of an MTC. At each step, studies that were dissimilar or contributed to substantial heterogeneity or inconsistency were excluded from the primary analysis. In a comparison of the MTC estimates from the consistent network with the MTC estimates from the homogeneous network including inconsistencies, few were affected by notable changes; that is, a change in effect size (factor 2), direction of effect or statistical significance. Considering the small proportion of studies excluded from the network due to inconsistency, as well as the number of notable changes, the MTC results were deemed sufficiently robust. In the absence of standard methods, our approach to checking assumptions in MTCs may inform other researchers in need of practical options, particularly in HTA.

Indirect Comparisons and Network Meta-Analyses.

BACKGROUND: Systematic reviews provide a structured summary of the results of trials that have been carried out on any particular subject. If the data from multiple trials are sufficiently homogenous, a meta-analysis can be performed to calculate pooled effect estimates. Traditional meta-analysis involves groups of trials that compare the same two interventions directly (head to head). Lately, however, indirect comparisons and network metaanalyses have become increasingly common. METHODS: Various methods of indirect comparison and network meta-analysis are presented and discussed on the basis of a selective review of the literature. The main assumptions and requirements of these methods are described, and a checklist is provided as an aid to the evaluation of published indirect comparisons and network meta-analyses. RESULTS: When no head-to-head trials of two interventions are available, indirect comparisons and network metaanalyses enable the estimation of effects as well as the simultaneous analysis of networks involving more than two interventions. Network meta-analyses and indirect comparisons can only be useful if the trial or patient characteristics are similar and the observed effects are sufficiently homogeneous. Moreover, there should be no major discrepancy between the direct and indirect evidence. If trials are available that compare each of two treatments against a third one, but not against each other, then the third intervention can be used as a common comparator to enable a comparison of the other two. CONCLUSION: Indirect comparisons and network metaanalyses are an important further development of traditional meta-analysis. Clear and detailed documentation is needed so that findings obtained by these new methods can be reliably judged.

Absolute risks rather than incidence rates should be used to estimate the number needed to treat from time-to-event data.

BACKGROUND: When estimating the number needed to treat (NNT) from randomized controlled trials (RCTs) with time-to-event outcomes, varying follow-up times have to be considered. Two methods have been proposed, namely (1) inverting risk differences estimated by survival time methods (RD approach) and (2) inverting incidence differences (ID approach). STUDY DESIGN AND SETTING: A simulation study was conducted to compare the RD and the ID approaches regarding bias and coverage probability (CP) considering various distributions, baseline risks, effect sizes, and sample sizes. Additionally, the two approaches were compared by using two real data examples. RESULTS: The RD approach showed good estimation and coverage properties with only a few exceptions in the case of small sample sizes and small effect sizes. The ID approach showed considerable bias and low CPs in most of the considered data situations. CONCLUSIONS: Absolute risks estimated by means of survival time methods rather than incidence rates should be used to estimate NNTs in RCTs with time-to-event outcomes.

Unsolved issues of mixed treatment comparison meta-analysis: network size and inconsistency.

Indirect comparisons and mixed treatment comparison (MTC) meta-analyses are increasingly used in medical research. These methods allow a simultaneous analysis of all relevant interventions in a connected network even if direct evidence regarding two interventions is missing. The framework of MTC meta-analysis provides a flexible approach for complex networks. However, this method has yet some unsolved problems, in particular the choice of the network size and the assessment of inconsistency. In this paper, we describe the practical application of MTC meta-analysis by using a data set on antidepressants. We focus on the impact of the size of the chosen network and the assumption of consistency. A larger network is based on more evidence but may show inconsistencies, whereas a smaller network contains less evidence but may show no clear inconsistencies. A choice is required which network should be used in practice. In summary, MTC meta-analysis represents a promising approach; however, clear application standards are still lacking. Especially, standards for the identification of inconsistency and the way to deal with potential inconsistency are required. Copyright © 2012 John Wiley & Sons, Ltd.

A descriptive and model-based spatial comparison of the standardised mortality ratio and the age-standardised mortality rate.

The number of deaths in a particular connection can be expressed in different ways. In spatial epidemiology, two widely used measures are the standardised mortality ratio (SMR) and the so called mortality rate. This paper compares these two ways of expressing mortality using a descriptive and a model-based approach. Age-standardised versions of both terms have been investigated by a descriptive analysis of temporal and spatial patterns and by employing different Bayesian spatial models to study their performance. We observed that the SMR and the age-standardised mortality rate (ASM) are strongly correlated and lead to comparable results. This demonstration is based on mortality data by age, stratified into five-year ranges, from the cause-of-death-statistics with reference to ischaemic heart disease and lung cancer in 54 counties of the German state of North Rhine Westphalia between 1980 and 1997.