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Ralf Bender

Publications and source records attributed to Ralf Bender.

At least 19 recordsLinked to original sources
PubMed2006

Calculating confidence intervals for impact numbers.

BACKGROUND: Standard effect measures such as risk difference and attributable risk are frequently used in epidemiological studies and public health research to describe the effect of exposures. Recently, so-called impact numbers have been proposed, which express the population impact of exposures in form of specific person or case numbers. To describe estimation uncertainty, it is necessary to calculate confidence intervals for these new effect measures. In this paper, we present methods to calculate confidence intervals for the new impact numbers in the situation of cohort studies. METHODS: Beside the exposure impact number (EIN), which is equivalent to the well-known number needed to treat (NNT), two other impact numbers are considered: the case impact number (CIN) and the exposed cases impact number (ECIN), which describe the number of cases (CIN) and the number of exposed cases (ECIN) with an outcome among whom one case is attributable to the exposure. The CIN and ECIN represent reciprocals of the population attributable risk (PAR) and the attributable fraction among the exposed (AFe), respectively. Thus, confidence intervals for these impact numbers can be calculated by inverting and exchanging the confidence limits of the PAR and AFe. EXAMPLES: We considered a British and a Japanese cohort study that investigated the association between smoking and death from coronary heart disease (CHD) and between smoking and stroke, respectively. We used the reported death and disease rates and calculated impact numbers with corresponding 95% confidence intervals. In the British study, the CIN was 6.46, i.e. on average, of any 6 to 7 persons who died of CHD, one case was attributable to smoking with corresponding 95% confidence interval of [3.84, 20.36]. For the exposed cases, the results of ECIN = 2.64 with 95% confidence interval [1.76, 5.29] were obtained. In the Japanese study, the CIN was 6.67, i.e. on average, of the 6 to 7 persons who had a stroke, one case was attributable to smoking with corresponding 95% confidence interval of [3.80, 27.27]. For the exposed cases, the results of ECIN = 4.89 with 95% confidence interval of [2.86, 16.67] were obtained. CONCLUSION: The consideration of impact numbers in epidemiological analyses provides additional information and helps the interpretation of study results, e.g. in public health research. In practical applications, it is necessary to describe estimation uncertainty. We have shown that the calculation of confidence intervals for the new impact numbers is possible by means of known methods for attributable risk measures. Therefore, estimated impact numbers should always be complemented by appropriate confidence intervals.

Cohort Studies↗
PubMed2006

Causes of death in obesity: relevant increase in cardiovascular but not in all-cancer mortality.

BACKGROUND AND OBJECTIVE: To assess the relation between body mass index (BMI) and the risk of death from various causes in a prospective cohort study. METHODS: In 6,192 obese patients (BMI > or =25 kg/m(2)) with mean BMI 36.6 kg/m(2) (SD 6.1) and mean age 40.4 years (SD 12.9) who had been referred to the obesity clinic of the Heinrich-Heine-University Düsseldorf, Germany, between 1961 and 1994, there were 1,058 deaths from all causes during a median follow-up time of 14.8 years. We calculated standardized mortality ratios (SMRs) with 95% confidence intervals (CIs) for death from predefined groups of diseases by using Germany as reference population. RESULTS: In both sexes, risk of death from cardiovascular diseases (men: SMR = 2.2, CI 1.9-2.5; women: SMR = 1.6, CI 1.5-1.8), from diabetes (men: SMR = 5.4, CI 3.2-8.7; women: SMR = 3.5, CI 2.6-4.8), and in men from digestive diseases (SMR = 1.6, CI 1.01-2.3) was significantly increased. In contrast to other studies, an association between obesity and all-cancer mortality could not be found. Only in morbidly obese women (BMI > or =40 kg/m(2)), all-cancer mortality was significantly increased (SMR = 1.5, CI 1.1-1.9). CONCLUSION: Obesity is associated with increased risk of death from cardiovascular diseases and diabetes in both sexes, and from diseases of the digestive system in men.

Adolescent↗
PubMed2006

[Assessment of the number of cardio- and cerebrovascular events due to rofecoxib (Vioxx) in Germany between 2001 and 2004].

BACKGROUND AND PURPOSE: After the recall of rofecoxib (Vioxx), there was repeated national and international discussion on the potential number of patients harmed by causally related cardio- and cerebrovascular events. In individual cases, it cannot be determined whether a myocardial infarction or stroke that occurred during rofecoxib therapy was actually directly caused by this drug. On the basis of the results of the Vioxx Gastrointestinal Outcomes Research (VIGOR) trial and German prescription data provided by the Scientific Institute of the Local Health Care Fund, the authors therefore conservatively estimated the number of patients harmed by rofecoxib in Germany between 2001 and 2004. METHODS: Under simplifying assumptions that, as in the VIGOR study, the risk of rofecoxib or naproxen therapy can be described by a Cox model with exponentially distributed event times, it is possible to calculate the daily risk of cardio- and cerebrovascular events in patients treated with these drugs. The estimated number of patients experiencing cardio- and cerebrovascular events under rofecoxib or naproxen therapy can be calculated by multiplying the daily risks by the defined daily doses prescribed in Germany. The difference between these numbers produces the estimated number of patients harmed by rofecoxib. RESULTS: On the basis of the data pool, a total of 7,092 additional diseased or deceased patients due to rofecoxib therapy were estimated (95% confidence interval: 2,004-15,416). The simplifying assumptions made together with the underreporting of events in the VIGOR trial are more likely to lead to an underestimation than an overestimation of affected patients. When assessing the benefit-harm ratio of rofecoxib, it needs to be considered that its protective gastrointestinal effects were not assessed compared with the optimum long-term therapy. It can be assumed that a comparison of rofecoxib with a combination of nonsteroidal anti-inflammatory drugs (NSAIDs) and gastric mucosal barrier protectors (e. g., misoprostol) would not have shown an advantage in favor of rofecoxib therapy. CONCLUSION: The example of rofecoxib and the relatively high number of patients harmed by it in Germany indicate that, before widely prescribing a new drug, a more thorough assessment of the benefit-harm ratio of the drug is required as well as a stronger consideration of therapeutic alternatives and a timely conduct of meaningful clinical studies. The results of these studies should be promptly communicated in full to physicians and patients.

Adult↗
PubMed2006

Long-term bond between dual-polymerizing cementing agents and human hard dental tissue.

OBJECTIVES: To examine the long-term adhesion of seven dual-polymerizing cementing agents to human dentin in vitro. METHODS: Two hundred and eighty extracted non-carious human molars were ground flat to expose dentin surfaces. The bond strengths of cementing agents with their respective bonding systems were examined: one compomer cement (PermaCem), five resin cements (RelyX ARC, Panavia F, Variolink II, Nexus 2, Calibra) and one self-adhesive universal resin cement (RelyX Unicem). One subgroup (n=10) was tested after 150 days of storage in water at 37 degrees C (time t(1)), the other subgroup (n=10) was tested after 150 days of storage plus 37,500 thermal cycles (time t(2)). All specimens were stressed in shear at a constant crosshead speed of 0.5mm/min until failure. Statistical analysis was performed by ANOVA, taking effect interactions into account. The Tukey method was used for multiple paired comparisons (alpha=0.05). RESULTS: The three-way ANOVA (cementing agents, polymerization methods, times of measurements) showed Variolink II to have the highest strength at 9.9+/-4.5MPa. Values were slightly higher at t(1) (5.9+/-4.7MPa) than at t(2) (4.9+/-4.2MPa) (p=0.0044). Polymerization with light activation (6.5+/-5.1MPa) yielded higher strengths than polymerization without (4.3+/-3.3MPa) (p<0.0001). Separate two-way ANOVAs for t(1) and t(2) showed that the two main effects (cementing agent, polymerization method) and their interactions differed significantly. SIGNIFICANCE: Cementing agents/adhesive systems and the polymerization method influence the long-term bond to hard dental tissues.

Acid Etching, Dental↗
PubMed2006

Flexible intensive insulin therapy in adults with type 1 diabetes and high risk for severe hypoglycemia and diabetic ketoacidosis.

OBJECTIVE: Diabetes treatment and teaching programs (DTTPs) for type 1 diabetes, which teach flexible intensive insulin therapy to enable dietary freedom, have proven to be safe and effective in routine care. This study evaluates DTTP outcomes in patients at high risk for severe hypoglycemia and severe ketoacidosis. RESEARCH DESIGN AND METHODS: There were 96 diabetes centers that participated between 1992 and 2004. A total of 9,583 routine-care patients with type 1 diabetes were examined before and 1 year after a DTTP. History of repeated severe hypoglycemia/severe ketoacidosis was an indication for DTTP participation. Before-after analyses were performed for subgroups of patients with three or more episodes of severe hypoglycemia or two or more episodes of severe ketoacidosis during the year before a DTTP. Main outcome measures were GHb, severe hypoglycemia, severe ketoacidosis, and hospitalization. RESULTS: A total of 341 participants had three or more episodes of severe hypoglycemia the year before a DTTP. Mean baseline GHb was 7.4 vs. 7.2% after the DTTP, incidence of severe hypoglycemia was 6.1 vs. 1.4 events x patient(-1) x year(-1), and hospitalization was 8.6 vs. 3.9 days x patient(-1) x year(-1). In mixed-effects models taking effects of centers and diabetes duration into account, mean difference was -0.3% (95% CI -0.5 to -0.1%; P = 0.0006) for GHb and -4.7 events x patient(-1) x year(-1) (-5.4 to -4; P < 0.0001) for severe hypoglycemia. A total of 95 patients had two or more episodes of severe ketoacidosis. GHb was 9.4% at baseline versus 8.7% after DTTP; incidence of severe ketoacidosis was 3.3 vs. 0.6 events x patient(-1) x year(-1), and hospitalization was 19.4 vs. 10.2 days x patient(-1) x year(-1). In linear models with diabetes duration as the fixed effect, the adjusted mean difference was -2.7 events x patient(-1) x year(-1) (95% CI -3.3 to -2.1; P < 0.0001) for severe ketoacidosis and -8.1 days (-12.9 to -3.2; P = 0.0014) for hospitalization. CONCLUSIONS: Patients at high risk for severe hypoglycemia or severe ketoacidosis may benefit from participation in a standard DTTP for intensive insulin therapy and dietary freedom.

Adult↗
PubMed2006

[Possibilities and limitations of statistical regression models for the calculation of threshold values for minimum provider volumes].

Inadequate statistical procedures are often applied for the derivation of threshold values in various medical research areas. The frequently applied method to establish threshold values on the basis of simple comparisons between arbitrarily defined low-volume and high-volume groups may be misleading because the result depends on the preceding classification. In this paper, the possibilities and limitations of statistical regression models for the calculation of threshold values are described. The features of these models for the selection of minimum volumes for hospitals or physicians are discussed. Simulated data examples are used to demonstrate that the definition of a useful minimum provider volume should not be based upon a calculated value of purely mathematical meaning without clinically assessing the risk curve. In the application of statistical regression models to retrospective observational data it should be noticed that calculated threshold values are only of a hypothesis-generating character. In order to verify that a minimum provider volume leads to the expected quality improvement, a prospective intervention study is required.

Data Interpretation, Statistical↗
PubMed2005

Predicting the risk of falling--efficacy of a risk assessment tool compared to nurses' judgement: a cluster-randomised controlled trial [ISRCTN37794278].

BACKGROUND: Older people living in nursing homes are at high risk of falling because of their general frailty and multiple pathologies. Prediction of falls might lead to an efficient allocation of preventive measures. Although several tools to assess the risk of falling have been developed, their impact on clinically relevant endpoints has never been investigated. The present study will evaluate the clinical efficacy and consequences of different fall risk assessment strategies. STUDY DESIGN: Cluster-randomised controlled trial with nursing home clusters randomised either to the use of a standard fall risk assessment tool alongside nurses' clinical judgement or to nurses' clinical judgement alone. Standard care of all clusters will be optimised by structured education on best evidence strategies to prevent falls and fall related injuries. 54 nursing home clusters including 1,080 residents will be recruited. Residents must be > or = 70 years, not bedridden, and living in the nursing home for more than three months. The primary endpoint is the number of participants with at least one fall at 12 months. Secondary outcome measures are the number of falls, clinical consequences including side effects of the two risk assessment strategies. Other measures are fall related injuries, hospital admissions and consultations with a physician, and costs.

Accidental Falls↗
PubMed2005

Generating survival times to simulate Cox proportional hazards models.

Simulation studies present an important statistical tool to investigate the performance, properties and adequacy of statistical models in pre-specified situations. One of the most important statistical models in medical research is the proportional hazards model of Cox. In this paper, techniques to generate survival times for simulation studies regarding Cox proportional hazards models are presented. A general formula describing the relation between the hazard and the corresponding survival time of the Cox model is derived, which is useful in simulation studies. It is shown how the exponential, the Weibull and the Gompertz distribution can be applied to generate appropriate survival times for simulation studies. Additionally, the general relation between hazard and survival time can be used to develop own distributions for special situations and to handle flexibly parameterized proportional hazards models. The use of distributions other than the exponential distribution is indispensable to investigate the characteristics of the Cox proportional hazards model, especially in non-standard situations, where the partial likelihood depends on the baseline hazard. A simulation study investigating the effect of measurement errors in the German Uranium Miners Cohort Study is considered to illustrate the proposed simulation techniques and to emphasize the importance of a careful modelling of the baseline hazard in Cox models.

Cohort Studies↗
PubMed2005

Tutorial: using confidence curves in medical research.

Confidence intervals represent a routinely used standard method to document the uncertainty of estimated effects. In most cases, for the calculation of confidence intervals the conventional fixed 95% confidence level is used. Confidence curves represent a graphical illustration of confidence intervals for confidence levels varying between 0 and 100%. Although such graphs have been repeatedly proposed under different names during the last 40 years, confidence curves are rarely used in medical research. In this paper, we introduce confidence curves and present a short historical review. We draw attention to the different interpretation of one- and two-sided statistical inference. It is shown that these two options also have influence on the plotting of appropriate confidence curves. We illustrate the use of one- and two-sided confidence curves and explain their correct interpretation. In medical research more emphasis on the choice between the one- and two-sided approaches should be given. One- and two-sided confidence curves are useful complements to the conventional methods of presenting study results.

Animals↗
PubMed2005

Eight-year trends in food, energy and macronutrient intake in a sample of elderly German subjects.

Time trends in the food and the corresponding energy and macronutrient intake between 1994 and 2002 are investigated as part of the longitudinal study on nutrition and health status in an ageing population in Giessen, Germany (GISELA study). The dietary intake is assessed via a 3 d estimated dietary record especially developed and validated for this study. A total of 2135 records from 532 subjects, aged 60 years and over, are analysed separately according to sex and age groups (born 1904-1928 and born 1929-1942). Results show that the food, energy and macronutrient intake of the GISELA subjects stayed fairly stable over the study period. However, some significant changes in the consumption pattern are observed, predominantly in the women and the younger age groups, which correspond to the national trends in Germany. Most obvious changes observed among the GISELA subjects are the increased intake of water (between +21.05 and +41.61 ml/d per year) and vegetables (between +2.94 and +3.38 g/d per year) and a reduced consumption of coffee and tea (between -10.65 and -15.99 ml/d per year) as well as of meat (between -1.79 and -2.56 g/d per year). The healthier food choices and the ability to change food habits could be related to the relatively high health-awareness of the GISELA subjects compared to the federal average of equivalent age groups.

Age Factors↗
PubMed2004

Predictors of adherence to the use of hip protectors in nursing home residents.

OBJECTIVES: To assess predictors of hip-protector use in nursing home residents under usual-care conditions and after intervention consisting of structured education of nurses and nursing home residents and provision of free hip protectors. DESIGN: Nested cohort analyses within a cluster randomized, controlled trial with 18 months follow-up. SETTING: Forty-nine nursing home clusters in Hamburg, Germany. PARTICIPANTS: Residents with at least one fall during the study period (intervention group, n=237; usual-care group, n=274). MEASUREMENTS: Use of hip protector while falling. Regression analyses were performed for each of the two cohorts of fallers using the time to the first fall without hip protector as the dependent variable. Predefined nursing home cluster-related parameters (center, staffing ratio, proportion of registered nurses in nursing staff, hip-protector use before study period) and resident-related parameters (sex, history of falls and fractures, fear of falling, urinary incontinence, use of walking aid, degree of disablement) were considered as explanatory variables. RESULTS: Under usual care, 97% of fallers (n=266), compared with 62% (n=148) in the intervention group, experienced at least one fall without hip protection. Using Cox proportional hazards models with and without frailty parameter (random cluster effect), the following predictors were identified: intervention group: use of walking aid, hazard ratio (HR)=1.53 (95% confidence interval (CI):0.98-2.39) and no urinary incontinence, HR=1.47 (95% CI:1.03-2.09); usual care: nursing staff per 10 residents, HR=0.78 (95% CI=0.63-0.96); high degree of disablement, HR=1.38 (95% CI=1.06-1.80); strong fear of falling, HR=0.78 (95% CI=0.60-1.02). The nursing home cluster was a significant predictor in the control group (P=.029), but not in the intervention group (P=.100). CONCLUSION: Only a few and weak predictors of hip-protector use of questionable relevance could be identified in both groups. Future research should concentrate on the implementation of interventions of proven efficacy, such as provision of hip protectors combined with structured education of staff and residents.

Accidental Falls↗
PubMed2004

The impact of non-compliance with the therapeutic regimen on the development of stroke among hypertensive men and women in Gaza, Palestine.

OBJECTIVE: Hypertension and stroke are 2 major public health problems worldwide. Several biological and non-biological risk factors for stroke have been identified in the past. Little is known regarding risk factors for stroke among the Arabic population in Gaza. To identify potential risk factors we investigated compliance with the therapeutic regimen and life style factors which may increase the risk for stroke. METHODS: To research this study question, a pair matched case control study was conducted in Gaza Strip (Shefa Hospital, Nasser Hospital, Khan Younis Hospital, and related primary health care clinics) in 2001 (from January through to December) among 112 patients, who had been hospitalized for acute stroke and history of hypertension, and 224 controls with history of hypertension from primary health care clinics. RESULTS: Conditional logistic regression models show significant associations between stroke and medication not taking as prescribed (odds ratio (OR)=6.07; 95% confidence interval (CI)=1.53, 24.07), using excessive salt at meals (OR=4.51; 95% CI=2.05, 9.90), eating diet high in fat (OR=4.67; 95% CI=2.09, 10.40), and high levels of stress (OR=2.77; 95% CI=1.43, 5.38). No significant association between smoking and the development of stroke (OR=2.12; 95 CI 0.82, 5.51) was found. Regular physical exercise was a protective factor (OR=0.26; 95% CI=0.12, 0.57). CONCLUSION: Our results on risk factors for stroke confirm several other studies. In future programs on health promotion among hypertensive men and women in Gaza these modifiable risk factors could be addressed by health education strategies.

Acute Disease↗
PubMed2003

Helicobacter pylori and carcinogenesis of gastric B-cell lymphomas.

Primary non-Hodgkin's lymphomas of the stomach are associated with Helicobacter pylori infection. We analyzed gastric lymphoma onset data with respect to prior H. pylori infections based on the multistage theory of carcinogenesis. This theory provides a link between epidemiological data and biological processes. The study involved 133 patients, aged 29-75 years, diagnosed with marginal zone B-cell lymphoma (MZBL) and diffuse large cell B-cell lymphoma (DLBL). A 2-parametric Weibull model was applied to MZBL and DLBL onset data. Median age of diagnosis of MZBL (DLBL) was 59 years (55 years) in males and 65.5 years (64 years) in females. Infection with H. pylori was found in 81.3% (59.5%) of the patients diagnosed with MZBL (DLBL). Lymphoma latency data were fitted to Weibull distributions with a shape parameter of 5.7 for MZBL cases and 4.2 for DLBL. The shape parameter that indicates the number of steps in carcinogenesis was approximately independent of the status of infection with H. pylori in DLBL in contrast to MZBL. It was shown that gastric lymphoma onset data can be described by Weibull distribution functions. The findings support the hypothesis that MZBL and DLBL have different lines of development. There is indication of stronger antigen dependency in the carcinogenesis of MZBL in comparison to DLBL.

Adult↗
PubMed2003

Breastfeeding promotion in non-UNICEF-certified hospitals and long-term breastfeeding success in Germany.

AIM: To assess breastfeeding practices using the World Health Organization/United Nations Children's Fund (WHO/UNICEF) Ten Steps to Successful Breastfeeding for Baby-Friendly Hospitals in unselected non-UNICEF certified German hospitals and to examine the influences of breastfeeding promotion on long-term breastfeeding success as assessed by WHO criteria. METHODS: Information on the fulfilment of the Ten Steps was collected in 177 randomly chosen maternity hospitals by a postal questionnaire. Breastfeeding duration was assessed in 1487 mothers delivering in these hospitals. Multiple logistic regression was used to estimate the association between a low breastfeeding promotion index, defined as fulfilment of fewer than five steps, and the risk of short-term breastfeeding, less than 4 mo. RESULTS: A higher breastfeeding promotion index was not associated with early breastfeeding but was significantly associated with full breastfeeding at 4 and 6 mo. After adjusting for confounding factors, delivering in a hospital with a low breastfeeding promotion index was associated with an increased risk of short-term breastfeeding [odds ratio (OR) 1.24], although associations with maternal demographic variables (young age: OR 3.34), low educational level (OR 2.81) and upbringing in East Germany (OR 2.27) were stronger. CONCLUSION: In unselected German hospitals even moderate levels of breastfeeding promotion identified by WHO/UNICEF criteria were associated with long-term breastfeeding success.

Adult↗
PubMed2002

Body weight, blood pressure, and mortality in a cohort of obese patients.

The associations between body weight, raised blood pressure, and mortality remain controversial. The authors examined these relations by considering all degrees of obesity in the Düsseldorf Obesity Mortality Study (1961-1994). Among 6,193 obese German patients aged 18-75 years and having a body mass index (BMI) of > or =25 kg/m(2), 1,059 deaths were observed after a median follow-up of 14.8 years. The entire cohort was grouped into quartiles according to BMI (25-<32, 32-<36, 36-<40, > or =40 kg/m(2)) and systolic blood pressure (SBP) (<140, 140-<160, 160-<180, > or =180 mmHg). Cox proportional hazards analyses were performed to adjust for age. For women, the mortality risk curves for the four BMI groups in relation to SBP were flat without crossing, whereas the risk curve for moderately obese men (BMI 25-<32 kg/m(2)) crossed the risk curves for the higher BMI groups. In the group of patients with very high blood pressure (SBP > or = 180 mmHg), moderately obese subjects (BMI 25-<32 kg/m(2)) had a higher mortality risk for men when compared with the BMI group 32-<36 kg/m(2) (hazard ratio =1.62, 95% confidence interval: 1.0, 2.7) but not for women (hazard ratio = 0.71, 95% confidence interval: 0.4, 1.2). These findings support previous observations that the risk of death is lower for hypertensive men in high compared with low BMI groups.

Adolescent↗
PubMed2002

Calculating the "number needed to be exposed" with adjustment for confounding variables in epidemiological studies.

The number needed to treat (NNT) is a popular summary statistic to describe the absolute effect of a new treatment compared with a standard treatment or control concerning the risk of an adverse event. The NNT concept can be applied whenever the risk of an adverse event is compared between two groups; for the comparison of exposed with unexposed subjects in epidemiological studies, we propose the term "number needed to be exposed" (NNE). Whereas in randomized clinical trials NNT can be calculated on the basis of a simple 2 x 2 table, in epidemiological studies methods to adjust for confounders are required in most applications. We derive a method based upon multiple logistic regression analysis to perform point and interval estimation of NNE with adjustment for confounding variables. The adjusted NNE can be calculated from the adjusted odds ratio (OR) and the unexposed event rate (UER) estimated by means of an appropriate multiple logistic regression model. As UER is dependent on the confounders, the adjusted NNEs also vary with the values of the confounding variables. Two methods are proposed to take the dependence of NNE on the values of the confounders into account. The adjusted number needed to be exposed can be a useful complement to the commonly presented results in epidemiological studies, such as ORs and attributable risks.

Clinical Trials as Topic↗