Olaf Gefeller

Friedrich-Alexander Universität Erlangen-Nürnberg, Erlangen, Bavaria, Germany

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Publications (241)782.3 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Patch test results often vary between departments, and also between countries. Such variation may be partly attributable to systematic effects introduced by patient characteristics, differing exposures, patient selection, or methodological differences. To examine the amount of variation of patient characteristics in terms of the MOAHLFA index and of the proportion of patients with at least one positive reaction to the (European) baseline series ('P' measure), and to examine potential reasons for the variation. A retrospective analysis was performed of patch test data from 63 530 consultations collected by 53 departments from 12 countries participating in the European Surveillance System on Contact Allergies (ESSCA) ( www.essca-dc.org) between 2009 and 2012. Considerable variation in the prevalence of the MOAHLFA factors between departments was found, caused, for example, by differing specializations (e.g. occupational dermatology) or patient characteristics. Notable variation concerning the 'P' measure was observed; however, larger national networks (contributing to the ESSCA) tend to have quite similar ranges of this measure. Data from one department per country give valuable insights into the spectrum of contact allergy prevalence rates in that country, but are not as representative as national data pooled from several departments. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.
    Contact Dermatitis 05/2015; DOI:10.1111/cod.12409 · 3.62 Impact Factor
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    ABSTRACT: Measurement errors of medico-technical devices can be separated into systematic bias and random error. We propose a new method to address both simultaneously via generalized additive models for location, scale and shape (GAMLSS) in combination with permutation tests. More precisely, we extend a recently proposed boosting algorithm for GAMLSS to provide a test procedure to analyse potential device effects on the measurements. We carried out a large-scale simulation study to provide empirical evidence that our method is able to identify possible sources of systematic bias as well as random error under different conditions. Finally, we apply our approach to compare measurements of skin pigmentation from two different devices in an epidemiological study. © The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.
    Statistical Methods in Medical Research 04/2015; DOI:10.1177/0962280215581855 · 2.96 Impact Factor
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    ABSTRACT: Fragrances are among the most common contact sensitizers. Changes in exposure lead to subsequent changes of sensitization incidence; patterns of exposure may be reflected in certain surrogate markers such as affected anatomical site or occupation. The objective of this study was to provide current results on sensitization prevalences to the fragrance allergy screening markers of the patch test baseline series, on time trends and on risk factors associated with sensitization. Data of all patients tested between 1999 and 2012 with fragrance mix I (8% petrolatum (pet.) n = 130 325), fragrance mix II (14% pet., since 2005, n = 81 290), Myroxylon pereirae resin (25% pet., n = 130 258) and oil of turpentine (10% pet., n = 131 595), respectively, in the Information Network of Departments of Dermatology (IVDK, www.ivkd.org) were subject to descriptive and log-binomial regression analysis. Overall, 16.31% of patients had a positive patch test reaction to at least one of the four markers. The prevalence to each of the four single markers was 8.71, 4.87, 8.36 and 1.95%. A peculiar downward trend of FM I until around 2006/2007 with subsequent increase, both significant, was noted. Mostly, sensitization risk was higher in older patients and females, and was to a varying extent associated with certain anatomical sites. The mostly stable or even increasing time trends warrant further in-depth research into causative exposures, addressing the effectiveness of (self-) regulation, aggregate exposure and ‘cocktail effect’. Copyright © 2015 John Wiley & Sons, Ltd.
    Flavour and Fragrance Journal 04/2015; DOI:10.1002/ffj.3242 · 1.76 Impact Factor
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    ABSTRACT: The level of knowledge and awareness of skin cancer risks in parents of young children is largely unknown. The Erlangen Kindergarten study, which enrolled 3,129 parents of 3- to 6-year-old children in southern Germany, addressed this. The population-based survey found an overall high level of knowledge about skin cancer risks and strong support for the necessity of sun protection but identified two areas (role of intermittent sun exposure, sun protection on cloudy summer days) offering a target for improvement in future public health campaigns. © 2015 Wiley Periodicals, Inc.
    Pediatric Dermatology 04/2015; DOI:10.1111/pde.12572 · 1.52 Impact Factor
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    ABSTRACT: Malignant melanoma is a very rare paediatric tumour. This study was performed in order to understand clinical features and prognosis of malignant melanoma in children and adolescents. 443 patients ⩽18years of age with malignant melanoma were prospectively registered with the German Central Malignant Melanoma Registry between 1983 and 2011. Cases were collected from 58 participating centres. 276 paediatric cases with a follow-up >3months were evaluated for survival probabilities and prognostic factors by Kaplan-Meier method. Age of diagnosis ranged from 3months to 18years (median age 16years). The male to female ratio was 0.8 (202 male, 240 female). Most melanoma were located at the trunk (n=195) and the lower extremity (n=114). Patients with >3months of follow-up (median 55months) showed an overall survival (OS) of 94.8% in 5years. Survival according to tumour stage was 98.5% for stage I (n=190), 91.1% for stage II (n=39) and 53.0% for stage III/IV tumours (n=11). Worse outcome was seen in patients with nodular melanoma (OS 77.9%, n=42) compared to superficial spread histotype (OS 100%, n=138) or other histotype (OS 96.9%, n=88) (p<0.0001), in case of thicker tumours (Clark level IV or V, OS 87.1%, n=84) compared to thinner tumours (Clark level I, II, III, OS 99.1%, n=164) (p=0.0008) and in case of ulceration (OS 65.6%, n=17) compared to no ulceration (OS 99.2%, n=182). Patient and tumour characteristics in paediatric melanoma patients show no evident differences to adult melanoma cases. The same clinical approach as in adults should be used. Copyright © 2015 Elsevier Ltd. All rights reserved.
    European journal of cancer (Oxford, England: 1990) 03/2015; 51(7). DOI:10.1016/j.ejca.2015.02.014 · 4.82 Impact Factor
  • Das Gesundheitswesen 09/2014; 76(08/09). DOI:10.1055/s-0034-1386987 · 0.62 Impact Factor
  • Das Gesundheitswesen 09/2014; 76(08/09). DOI:10.1055/s-0034-1387053 · 0.62 Impact Factor
  • W Uter, A Pfahlberg, C Fießler, O Gefeller
    Das Gesundheitswesen 09/2014; 76(08/09). DOI:10.1055/s-0034-1387054 · 0.62 Impact Factor
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    ABSTRACT: Background Cobalt contact sensitization in consecutively tested patients is common. The sources of exposure, and thus clinical relevance, are mostly unclear.Objective To examine (i) long-term time trends of sensitization, (ii) risk factors that may point to relevant exposures, and (iii) coupling with nickel sensitization.Methods Data of all patients patch tested with cobalt(II) chloride hexahydrate (1% pet.) between 1992 and 2012 (n = 185 050) in the Information Network of Departments of Dermatology (IVDK, www.ivkd.org) were subjected to descriptive stratified and Poisson regression analysis.ResultsThe overall prevalence of positive patch test reactions was 5.23% (95% confidence interal 5.13–5.33%). Regarding time trends, there were significant increases for males aged 18–44 years and for females aged ≥45 years, and a significant variation of co-reactivity with nickel over time. Female sex almost doubled the risk of sensitization; age ≥45 years was associated with a 30% decrease in the risk of positive patch test reactions to cobalt, and atopic eczema with an approximately 20% increase.Conclusions Notwithstanding some diagnostic difficulties with the test preparation, a persistent, notable proportion of cobalt sensitization, isolated or coupled with nickel allergy, can be observed. This warrants further in-depth research into causative exposures, both at the workplace and in consumers.
    Contact Dermatitis 09/2014; 71(6). DOI:10.1111/cod.12284 · 3.62 Impact Factor
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    ABSTRACT: A high number of melanocytic naevi is one of the major risk factors for cutaneous melanoma. Therefore, counting the number of acquired naevi could be a useful strategy to identify individuals at an increased risk for targeted skin cancer screening. The aim of this study was to assess agreement between naevus self-counts and counts of trained examiners as well as to analyse potential determinants of the magnitude of agreement. In a large cross-sectional survey (n=1772), university students counted their naevi on both arms and were additionally examined by specifically trained examiners in a mutually blinded manner. Further data on other melanoma risk factors such as skin phototype, hair colour or freckling were collected by a questionnaire. The relative difference between the two naevus counts and the ratio of the counts were calculated to quantify agreement. Regression modelling was performed to identify independent determinants of agreement. The overall agreement was moderate, with participants counting on average 14% more naevi than the examiners. In terms of the potential determinants associated with agreement, skin type and medical education showed a strong effect. The difference in naevus counts was significantly larger for individuals with lighter skin types compared with those with a dark skin (Fitzpatrick type IV), and medical students yielded a naevus count more similar to the examiner's count than nonmedical students. Naevus self-counts can only provide a rough estimate of the number of naevi, but may not be accurate enough to reliably identify a high-risk group for melanoma screening, especially in individuals with light skin types.
    Melanoma Research 07/2014; 24(6). DOI:10.1097/CMR.0000000000000111 · 2.10 Impact Factor
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    ABSTRACT: Public health campaigns have improved knowledge on UVR-associated skin cancer risk and increased sun protection awareness. However, tanned skin is still a common beauty ideal. The relationship between knowledge, attitudes and protective behavior is not fully understood yet. A population-based survey was thus performed in the district of Erlangen involving 2,619 parents of 3- to 6-year old children. By means of a self-administered standardized questionnaire parental knowledge about risk factors for skin cancer, their attitudes towards tanning and details of protective measures taken for their children were assessed. The study analyzed specifically the impact of parental tanning attitudes on sun-protective measures for their children while controlling for parental knowledge about skin cancer risk factors. While parental knowledge was significantly (inversely) associated with agreement to the statement "Tanned skin is healthy skin", this was not the case for "Tanning makes me look better". Overall, tanning affirmative attitudes were inversely associated with protective measures taken for the children, whereas parental knowledge had a positive impact on sun protection at the beach only. Multivariable analyses provided evidence for an effect of parental attitude on protective behavior independent of parental knowledge. Tanning attitudes and tanned skin as the misguided ideal of beauty need to be addressed in future public health campaigns to enhance the effectiveness of preventive activities in changing sun protective behavior.
    International Journal of Environmental Research and Public Health 05/2014; 11(5):4768-81. DOI:10.3390/ijerph110504768 · 1.99 Impact Factor
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    ABSTRACT: Boosting algorithms to simultaneously estimate and select predictor effects in statistical models have gained substantial interest during the last decade. This review article aims to highlight recent methodological developments regarding boosting algorithms for statistical modelling especially focusing on topics relevant for biomedical research. We suggest a unified framework for gradient boosting and likelihood-based boosting (statistical boosting) which have been addressed strictly separated in the literature up to now. Statistical boosting algorithms have been adapted to carry out unbiased variable selection and automated model choice during the fitting process and can nowadays be applied in almost any possible type of regression setting in combination with a large amount of different types of predictor effects. The methodological developments on statistical boosting during the last ten years can be grouped into three different lines of research: (i) efforts to ensure variable selection leading to sparser models, (ii) developments regarding different types of predictor effects and their selection (model choice), (iii) approaches to extend the statistical boosting framework to new regression settings.
    Methods of Information in Medicine 03/2014; 53(5). DOI:10.3414/ME13-01-0123 · 1.08 Impact Factor
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    ABSTRACT: The concept of boosting emerged from the field of machine learning. The basic idea is to boost the accuracy of a weak classifying tool by combining various instances into a more accurate prediction. This general concept was later adapted to the field of statistical modelling. This review article attempts to highlight this evolution of boosting algorithms from machine learning to statistical modelling. We describe the AdaBoost algorithm for classification as well as the two most prominent statistical boosting approaches, gradient boosting and likelihood-based boosting. Although both appraoches are typically treated separately in the literature, they share the same methodological roots and follow the same fundamental concepts. Compared to the initial machine learning algorithms, which must be seen as black-box prediction schemes, statistical boosting result in statistical models which offer a straight-forward interpretation. We highlight the methodological background and present the most common software implementations.
    Methods of Information in Medicine 03/2014; 53(5). DOI:10.3414/ME13-01-0122 · 1.08 Impact Factor
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    ABSTRACT: Background Cosmetics for bleaching, waving/relaxing and dyeing hair contain well-known allergens, leading to a substantial number of cases of allergic contact dermatitis.Objective To compare the frequency of important contact allergens (i) between two distinct groups of exposed patients, and (ii) with previous surveillance data.Methods On the basis of data collected by the Information Network of Departments of Dermatology (IVDK; www.ivkd.org) between 2007 and 2012 in 824 female hairdressers and 2067 female clients, the current spectrum of contact sensitization to ingredients of hair cosmetics, as contained in different pertinent series, is described.ResultsA similar burden of sensitization as in previous analyses was observed, but with some increase in sensitization to oxidative hair dye components in clients. Some allergens mainly affected hairdressers, such as ammonium persulfate (18.7% positive) and glyceryl monothioglycolate (GMTG; still 4.7% positive, with a few cases also in young hairdressers, despite removal from the German market).Conclusions Hair dyes remain important contact allergens, despite various attempts by the cosmetic industry to introduce hair dyes with lower allergenic potential. The re-emergence of GMTG as an occupational allergen should be considered as a warning signal (‘sentinel event’) prompting close monitoring.
    Contact Dermatitis 03/2014; 71(1). DOI:10.1111/cod.12196 · 3.62 Impact Factor
  • Experimental and Clinical Endocrinology & Diabetes 11/2013; 121(10). DOI:10.1055/s-0033-1359430 · 1.76 Impact Factor
  • Cancer Research 08/2013; 73(8 Supplement):4687-4687. DOI:10.1158/1538-7445.AM2013-4687 · 9.28 Impact Factor
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    ABSTRACT: Hydroxyisohexyl 3-cyclohexene carboxaldehyde (HICC) is a synthetic fragrance chemical and an important contact allergen, at least in Europe. Despite this importance, little is known about risk factors associated with this allergen. To examine factors from the history and clinical presentation of patch tested patients associated with HICC sensitization. Contact allergy surveillance data of 95 637 patients collected by the Information Network of Departments of Dermatology (IVDK, www.ivkd.org) in 2002-2011 were analysed. Point and interval estimates of the relative risk were derived from multifactorial logistic regression modelling. The overall prevalence of HICC sensitization was 2.24%. The strongest risk factors were polysensitization and dermatitis of the axillae, followed by dermatitis at other sites. No consistent and significant time trend was observed in this analysis. As compared with the youngest patients, the odds of HICC sensitization increased approximately three-fold in the 52-67-year age group, and strongly declined with further increasing age. The risk pattern with regard to age and affected anatomical site differed from that observed with other fragrance screening allergens. Cosmetic exposure, as broadly defined here, was a stronger and more prevalent individual risk factor than occupational exposure.
    Contact Dermatitis 08/2013; 69(2):72-7. DOI:10.1111/cod.12069 · 3.62 Impact Factor
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    ABSTRACT: No observed event is a special, but not uncommon, result in patch test studies. The interpretation of such findings depends critically on the sample size (n) of the investigation, and is statistically addressed by the use of confidence intervals (CIs). To define the statistically correct method of calculating a CI with a confidence level of 1 - α, where α denotes the tolerated statistical error probability, for an observed prevalence of 0%. A literature survey and evaluation of the statistical methods was conducted. The popular statistical software packages spss™ and sas™ were examined with regard to the methods implemented, and the results obtained, for estimating such CIs in this special case. The evaluation identified [0; 1 - α(1/n) ], which is well approximated by [0; 3/n] for α = 0.05, as an appropriate method to compute a CI with a confidence level of 1 - α. The resulting CI is an exact one, and more efficient than standard solutions. Popular statistical software such as spss™ and sas™ offers only various inefficient or even invalid procedures, but does not include this method. It is easy to calculate a CI for an observed prevalence of 0% obtained in some studies. Such a CI facilitates the interpretation of such a finding, as it puts the observed zero result into adequate statistical perspective.
    Contact Dermatitis 07/2013; 69(6). DOI:10.1111/cod.12112 · 3.62 Impact Factor
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    ABSTRACT: Aim: The Material Values Scale is an instrument to assess beliefs about the importance to own material things. This instrument originally consists of the three subscales: ‘centrality’, ‘success’, and ‘happiness’. The present study investigated the psychometric properties of the German version of the MVS (G-MVS). Method: A population-based sample of 2,295 adult Germans completed the questionnaire in order to investigate the factorial structure. To test construct validity, additional samples were gathered among patients with compulsive buying (N=52) and medical students (N=347) who also answered the Compulsive Buying Scale (CBS) and the Patient Health Questionnaire depression scale (PHQ-8). Results: In the German population-based sample we could not confirm the 3-factor model but rather suggest a 2-factor solution with a first collapsed factor ‘centrality/success’, and the second factor ’happiness’. Patients with compulsive buying showed the highest scores on the G-MVS. While G-MVS scores among compulsive buyers and medical students were significantly related to compulsive buying scores, the correlation between the G-MVS and the depression measure appeared substantially lower. We did not find any gender differences regarding materialism, neither in the population-based sample nor in the students’ or compulsive buyers’ samples. However, age was negatively related to G-MVS scores. Conclusion: Confirmatory factor analyses suggest a 2-factor model of the G-MVS. Overall, the results indicate the use of the G-MVS as a brief, psychometrically sound, and potentially valid measure for the assessment of material values.
    06/2013; 10:Doc05. DOI:10.3205/psm000095
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    J Schwitulla, O Gefeller, A Schnuch, W Uter
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    ABSTRACT: BACKGROUND: "Polysensitisation" (PS) is usually defined as contact sensitisation to 3 or more unrelated haptens of the baseline patch test series. Despite PS being an important clinical phenotype indicating increased susceptibility to contact allergy, statistical approaches to analyse PS have hitherto been preliminary. OBJECTIVES: To apply an appropriate regression model for count data, namely, negative binomial hurdle regression, to a large set of clinical patch test data with the aim of estimating PS risk in more detail than previously achieved. METHODS: The detailed information provided by the hurdle model includes a separate estimation of an 'increment factor' quantifying the likelihood of further positive reactions, i.e. PS. Clinical data of 126878 patients patch tested by departments comprising the IVDK network (www.ivdk.org) between 1995 and 2010 were included. RESULTS: Regarding anatomical sites as exposure (surrogate), the axillae and the feet were found to be strong PS risk factors. Moreover, age was a strong PS risk factor, and less so, female sex. In comparison, atopic eczema and occupational dermatitis were less important risk factors. Single allergens contributed to PS to a varying extent. CONCLUSION: The data presented point to some, very likely exposure-related, risk factors which need to be considered in future PS research, e.g., addressing the genetic basis for PS. This article is protected by copyright. All rights reserved.
    British Journal of Dermatology 05/2013; 169(3). DOI:10.1111/bjd.12423 · 4.10 Impact Factor

Publication Stats

5k Citations
782.30 Total Impact Points

Institutions

  • 1999–2015
    • Friedrich-Alexander Universität Erlangen-Nürnberg
      • Department of Medical Informatics, Biometry and Epidemiology
      Erlangen, Bavaria, Germany
  • 1999–2014
    • Universitätsklinikum Erlangen
      Erlangen, Bavaria, Germany
  • 2008
    • Technische Universität Dortmund
      • Department of Business and Social Statistics
      Dortmund, North Rhine-Westphalia, Germany
  • 1992–2006
    • Georg-August-Universität Göttingen
      • Department of Clinical Psychology and Psychotherapy
      Göttingen, Lower Saxony, Germany
    • Norwegian Business School
      Kristiania (historical), Oslo, Norway
  • 2005
    • University of Greifswald
      • Center for Internal Medicine
      Griefswald, Mecklenburg-Vorpommern, Germany
  • 2004–2005
    • Universität Heidelberg
      Heidelburg, Baden-Württemberg, Germany
    • University of Helsinki
      • Department of Dental Public Health
      Helsinki, Uusimaa, Finland
  • 2002
    • University of Hamburg
      • Institute for Occupational and Maritime Medicine
      Hamburg, Hamburg, Germany
    • Tel Aviv University
      Tell Afif, Tel Aviv, Israel
  • 1997–2002
    • Universitätsmedizin Göttingen
      • Department of Medical Statistics
      Göttingen, Lower Saxony, Germany
    • Max Planck Institute for Experimental Medicine
      Göttingen, Lower Saxony, Germany
  • 1995–2001
    • Universität Osnabrück
      Osnabrück, Lower Saxony, Germany
    • Norges Handelshøyskole
      Bergen, Hordaland, Norway
  • 1994–1997
    • Universität Ulm
      Ulm, Baden-Württemberg, Germany
  • 1990
    • Ruhr-Universität Bochum
      • Abteilung für Schmerzmedizin
      Bochum, North Rhine-Westphalia, Germany