21 research outputs found
The Knight on the Threshold: a Thematic and Anthropological Study of the English Gawain Romances
No full textWillem van Zwet, teacher and thesis advisor
No full textWillem van Zwet was supervisor of sixteen PhD students. All of them pursued academic careers and most of them became full professor. Below are some stories of PhD students Wim Albers, Cees Diks, Ronald Does, Marta Fiocco, Sara van de Geer, Mathisca de Gunst, Chris Klaassen, Hein Putter, Aad van der Vaart, Marten Wegkamp and Martien van Zuijlen with in addition a contribution by Nelly Litvak who was guided by Willem after her PhD
Competing risks in epidemiology: possibilities and pitfalls.
No full textItem does not contain fulltextBACKGROUND: In studies of all-cause mortality, the fundamental epidemiological concepts of rate and risk are connected through a well-defined one-to-one relation. An important consequence of this relation is that regression models such as the proportional hazards model that are defined through the hazard (the rate) immediately dictate how the covariates relate to the survival function (the risk). METHODS: This introductory paper reviews the concepts of rate and risk and their one-to-one relation in all-cause mortality studies and introduces the analogous concepts of rate and risk in the context of competing risks, the cause-specific hazard and the cause-specific cumulative incidence function. RESULTS: The key feature of competing risks is that the one-to-one correspondence between cause-specific hazard and cumulative incidence, between rate and risk, is lost. This fact has two important implications. First, the naive Kaplan-Meier that takes the competing events as censored observations, is biased. Secondly, the way in which covariates are associated with the cause-specific hazards may not coincide with the way these covariates are associated with the cumulative incidence. An example with relapse and non-relapse mortality as competing risks in a stem cell transplantation study is used for illustration. CONCLUSION: The two implications of the loss of one-to-one correspondence between cause-specific hazard and cumulative incidence should be kept in mind when deciding on how to make inference in a competing risks situation.01 juni 201
Genome-wide meta-analysis identifies 11 new loci for anthropometric traits and provides insights into genetic architecture
No full textApproaches exploiting trait distribution extremes may be used to identify loci associated with common traits, but it is unknown whether these loci are generalizable to the broader population. In a genome-wide search for loci associated with the upper versus the lower 5th percentiles of body mass index, height and waist-to-hip ratio, as well as clinical classes of obesity, including up to 263,407 individuals of European ancestry, we identified 4 new loci (IGFBP4, H6PD, RSRC1 and PPP2R2A) influencing height detected in the distribution tails and 7 new loci (HNF4G, RPTOR, GNAT2, MRPS33P4, ADCY9, HS6ST3 and ZZZ3) for clinical classes of obesity. Further, we find a large overlap in genetic structure and the distribution of variants between traits based on extremes and the general population and little etiological heterogeneity between obesity subgroups
Bone structure changes in iliac crest grafts combined with implants
No full textRemodeling of onlay grafts combined with implants to the mandible results in predictable changes in the graft's radiographic density. We studied the relationship between changes in radiographic density and trabecular structure during the first year after onlay grafting with simultaneous implant placement to the mandible. The aim of this study was to evaluate changes in bone structure after onlay grafting. Standardized extraoral radiographs were taken regularly of 16 mandibular sides. Bone structure was measured using the Carl Zeiss Vision KS 400 3.0 imaging system. The parameters studied were trabecular area and perimeter, cavity area and perimeter, end points, branching points, skeleton length, branch angle and direction, and texture. No differences were found between measurements ventrally versus dorsally of the implant, nor close to versus away from the implant. Early cortical changes suggest partial resorption and formation of a more complex structure. In the fourth quarter after surgery, progressive resorption is seen in the graft's upper cortex. In the graft's upper spongiosa, most parameters indicate bone formation during the first postoperative year. Loading-induced structure changes could not yet be found. The technique can be used to study changes in the architecture of bone grafts. Changes found in the graft's architecture are in accordance with changes in bone densit
The common characteristics and outcomes of multidisciplinary collaboration in primary health care: a systematic literature review
No full textIntroduction: Research on collaboration in primary care focuses on specific diseases or types of collaboration. We investigate the effects of such collaboration by bringing together the results of scientific studies.Theory and methods: We conducted a systematic literature review of PubMed, CINAHL, Cochrane and EMBASE. The review was restricted to publications that test outcomes of multidisciplinary collaboration in primary care in high-income countries. A conceptual model is used to structure the analysis.Results: Fifty-one studies comply with the selection criteria about collaboration in primary care. Approximately half of the 139 outcomes in these studies is non-significant. Studies among older patients, in particular, report non-significant outcomes (p < .05). By contrast, a higher proportion of significant results were found in studies that report on clinical outcomes.Conclusions and discussion: This review shows a large diversity in the types of collaboration in primary care; and also thus a large proportion of outcomes do not seem to be positively affected by collaboration. Both the characteristics of the structure of the collaboration and the collaboration processes themselves affect the outcomes. More research is necessary to understand the mechanism behind the success of collaboration, especially on the exact nature of collaboration and the context in which collaboration takes place. </p
Comparison of Allogeneic Stem Cell Transplantation and Non-Transplant Approaches in Elderly Patients with Advanced Myelodysplastic Syndrome: Optimal Statistical Approaches and a Critical Appraisal of Clinical Results Using Non-Randomized Data
No full textAllogeneic stem cell transplantation (ASCT) from related or unrelated donors may cure patients with myelodysplastic syndromes (MDS), a heterogeneous group of clonal stem cell disorders. We analysed 384 elderly patients (55-69 years) with advanced MDS who received either ASCT (n=247) and were reported to The European Group for Blood and Marrow Transplantation (EBMT) or a non -transplant approach (n=137) reported to the Dusseldorf registry. Besides an attempt to answer the question of "comparison", the purpose of this work is to explain the difficulties in comparing a non-transplant with a transplant cohort, when death before transplant is likely but unknown and the selection of patients for transplant is based on assumptions. It shows which methods are almost always biased and that even the most sophisticated approaches crucially rely on clinical assumptions. Using the most appropriate model for our data, we derive an overall univariate non-significant survival disadvantage for the transplant cohort (HR: 1.29, p=0.11). We show that such an "average" hazard ratio is however misleading due to non-proportionality of the hazards reflecting early treatment related mortality, the occurring of which is logically correlated with the interval between diagnosis and transplant creating a disproportional drop in the (reconstructed) survival curve of the transplanted patients. Also in multivariate analysis (correcting for age > 60 (HR: 1.4, p=0.02) and abnormal cytogenetics (HR: 1.46, p=0.01)), transplantation seems to be worse (HR: 1.39, p=0.05) but only in the (incorrect but commonly applied) model without time varying covariates. The long term (time depending) hazard ratio is shown to be virtually 1 and overall survival is virtually identical in both groups. Nonetheless no conclusion can be reached from a clinical point of view without assumptions which are by their very nature untestable unless all patients would be followed from diagnosis
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The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: measurements of the growth of structure and expansion rate at z=0.57 from anisotropic clustering
No full textWe analyse the anisotropic clustering of massive galaxies from the Sloan Digital Sky Survey III Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 9 (DR9) sample, which consists of 264 283 galaxies in the redshift range 0.43 0.57, and when combined imply OmegaLambda = 0.74 ± 0.016, independent of the Universe's evolution at z < 0.57. All of these constraints assume scale-independent linear growth, and assume general relativity to compute both O(10 per cent) non-linear model corrections and our errors. In our companion paper, Samushia et al., we explore further cosmological implications of these observations
Fetal Origins, Childhood Development, and Famine: A Bibliography and Literature Review
No full textThe human costs of famines outlast the famines themselves. An increasing body of research points to their adverse long-run consequences for those born or in utero during them. This paper offers an introduction to the burgeoning literature on fetal origins and famine through a review of research on one well-known case study and a bibliography of published work in the field generally.health, famine, fetal origins, economic history
