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Guido Schwarzer

Publications and source records attributed to Guido Schwarzer.

13 recordsLinked to original sources
PubMed2007

A test for publication bias in meta-analysis with sparse binary data.

A new test for the detection of publication bias in meta-analysis with sparse binary data is proposed. The test statistic is based on observed and expected cell frequencies, and the variance of the observed cell frequencies. These quantities are utilized in a rank correlation test. Type I error rate and power of the test are evaluated in simulations; results are compared to those of two other commonly used test procedures. Sample sizes were generated according to findings in a survey of eight German medical journals. Simulation results indicate that, in contrast to existing test procedures, the new test holds the prescribed significance level when data are sparse. However, the power of all tests is low in many situations of practical importance.

Anemia↗
PubMed2006

The demise of the randomised controlled trial: bibliometric study of the German-language health care literature, 1948 to 2004.

BACKGROUND: In order to reduce systematic errors (such as language bias) and increase the precision of the summary treatment effect estimate, a comprehensive identification of randomised controlled trials (RCT), irrespective of publication language, is crucial in systematic reviews and meta-analyses. We identified trials in the German general health care literature. METHODS: Eight German language general health care journals were searched for randomised controlled trials and analysed with respect to the number of published RCTs each year and the size of trials. RESULTS: A total of 1618 trials were identified with a median total number of 43 patients per trial. Between 1970 and 2004 a small but constant rise in sample size from a median number of 30 to 60 patients per trial can be observed. The number of published trials was very low between 1948 and 1970, but increased between 1970 and 1986 to a maximum of 11.2 RCTs per journal and year. In the following time period a striking decline of the number of RCTs was observed. Between 1999 and 2001 only 0.8 RCTs per journal and year were published, in the next three years, the number of published trials increased to 1.7 RCTs per journal and year. CONCLUSION: German language general health care journals no longer have a role in the dissemination of trial results. The slight rise in the number of published RCTs in the last three years can be explained by a change of publication language from German to English of three of the analysed journals.

Bibliometrics↗
PubMed2006

Single-agent purine analogues for the treatment of chronic lymphocytic leukaemia: a systematic review and meta-analysis.

BACKGROUND: Recent trials suggest improved response rates for purine analogues compared to alkylator-based regimens in the treatment of B-CLL. However, none was able to show a survival advantage. Thus, a systematic Cochrane review may be able to further define the role of purine analogues in the first-line treatment of B-CLL. METHODS: Randomized controlled trials comparing single-agent purine analogues with alkylator-based regimens were included. Medical databases (Cochrane Library, MEDLINE, EMBASE), conference proceedings and trial registers were searched. We included full-text and abstract publications as well as unpublished data. Relative risks (RR) and hazard ratios (HR) were calculated under a fixed-effects model, clinical and statistical heterogeneity was examined with sensitivity analyses and meta-regression. If applicable, numbers needed to treat or harm (NNT, NNH) were also determined. FINDINGS: Five trials with 1838 randomized patients were included. Importantly, four trials had a cross-over design. There was a trend for improved overall survival for patients receiving purine analogues as initial therapy but statistical significance was just not reached (HR 0.89 [95% CI 0.78-1.01]). The RR for achieving an overall (RR 1.22 [95% CI 1.13-1.31]; NNT 8 [95% CI 6-13]) and complete response (RR 1.94 [95% CI 1.65-2.28]; NNT 6 [5-8]) was significantly improved, resulting in a longer progression-free survival (HR 0.70 [95% CI 0.61-0.82]). Incidence of grade III/IV infections (RR 1.83 [95% CI 1.30-2.58]; NNH 20 [95% CI 12.5-50]) and haemolytic anaemia (RR 3.36 [95% CI 1.27-8.91]; NNH 21 [95% CI 6-185]) was significantly higher in patients receiving purine analogues. INTERPRETATION: Despite significantly increased response rates and longer progression-free survival with purine analogues as first-line therapy, we were not able to detect a statistically significant improvement of overall survival compared to alkylator-based regimens. Furthermore, the use of purine analogues augments the risk for grade III/IV infections and haemolytic anaemia.

Anemia, Hemolytic↗
PubMed2006

Recombinant human erythropoietins and cancer patients: updated meta-analysis of 57 studies including 9353 patients.

This is an updated systematic review of 57 trials and 9353 cancer patients from articles, abstracts, and reports published between January 1, 1985, and April 30, 2005, on the effects of epoetin alfa and beta (i.e., epoetin) and darbepoetin alfa (i.e., darbepoetin). We included randomized controlled trials comparing epoetin or darbepoetin plus red blood cell transfusion with red blood cell transfusion alone for prophylaxis or treatment of anemia in cancer patients with or without concurrent antineoplastic therapy. The Cochrane Library, MEDLINE, EMBASE, and conference proceedings were searched. Effect estimates and 95% confidence intervals (CIs) were calculated with fixed-effects models. Treatment with epoetin or darbepoetin statistically significantly reduced the risk for red blood cell transfusions (relative risk [RR] = 0.64, 95% CI = 0.60 to 0.68; 42 trials and 6510 patients) and improved hematologic response (RR = 3.43, 95% CI = 3.07 to 3.84; 22 trials and 4307 patients). Treatment with epoetin or darbepoetin increased the risk of thrombo-embolic events (RR = 1.67, 95% CI = 1.35 to 2.06; 35 trials and 6769 patients). Uncertainties remain as to whether and how epoetin or darbepoetin affects overall survival (hazard ratio = 1.08, 95% CI = 0.99 to 1.18; 42 trials and 8167 patients). Caution is advised when using epoetin or darbepoetin in combination with thrombogenic chemotherapeutic agents or for cancer patients who are at high risk for thrombo-embolic events.

Anemia, Hypochromic↗
PubMed2005

Treatment of ocular hypertension and open angle glaucoma: meta-analysis of randomised controlled trials.

OBJECTIVE: Open angle glaucoma is one of the most common causes of blindness in industrialised nations. Treatments to lower ocular pressure are widely used in glaucoma prevention and treatment, despite conflicting evidence. DESIGN: We performed meta-analyses to reassess the effectiveness of pressure lowering treatment to delay the development of glaucoma in ocular hypertension, as well as progression of manifest open angle glaucoma. DATA SOURCES: Medline, Embase, and the Cochrane Library. SELECTION OF STUDIES: Eligible studies were randomised controlled trials with a concurrent untreated control group and information on time to glaucomatous changes to visual field and optic disc. Trial reports were reviewed independently by two investigators in an unblinded standardised manner. RESULTS: Meta-analysis of trials in ocular hypertension showed a significant preventive effect of reducing intraocular pressure on progression to glaucoma (hazard ratio 0.56, 95% confidence interval 0.39 to 0.81, P = 0.01; number needed to treat 12). Pooled data of studies in manifest glaucoma showed a significant delay of visual field deterioration (0.65, 0.49 to 0.87, P = 0.003; NNT = 7), with subgroup analysis showing a larger effect in patients with raised pressure and a reduced effect in normal tension glaucoma (subgroup comparison: not significant). CONCLUSIONS: Lowering intraocular pressure in patients with ocular hypertension or manifest glaucoma is beneficial in reducing the risk of visual field loss in the long term.

Glaucoma, Open-Angle↗
PubMed2005

Recombinant human erythropoietin and overall survival in cancer patients: results of a comprehensive meta-analysis.

BACKGROUND: Anemia associated with cancer and cancer therapy is an important clinical and economic factor in the treatment of malignant diseases. METHODS: We conducted a systematic literature review to assess the efficacy of erythropoietin to prevent or treat anemia in cancer patients with regard to red blood cell transfusions, hematologic response, adverse events, and overall survival. We searched the Cochrane Library, Medline, EMBASE, and other databases for relevant articles published from January 1985 to December 2001. We included all randomized controlled trials that compared the use of recombinant human erythropoietin (plus transfusion, if needed) with no erythropoietin treatment (plus transfusion, if needed). Relative risks (RRs) and 95% confidence intervals (CIs) were calculated under a fixed-effects model. Clinical and statistical heterogeneity were examined with sensitivity analyses and meta-regression. Statistical tests for effect estimates were two-sided. RESULTS: We identified 27 trials involving 3287 adult patients. Patients treated with erythropoietin had a lower relative risk of having a blood transfusion than untreated patients (RR = 0.67, 95% CI = 0.62 to 0.73). Erythropoietin-treated patients with baseline hemoglobin levels lower than 10 g/dL were more likely to have a hematologic response than untreated patients (RR = 3.60, 95% CI = 3.07 to 4.23). The relative risk for thromboembolic complications after erythropoietin treatment was not statistically significantly increased (RR = 1.58, 95% CI = 0.94 to 2.66) compared with that of untreated patients. There is suggestive but inconclusive evidence that erythropoietin may improve overall survival (adjusted data: hazard ratio [HR] = 0.81, 95% CI = 0.67 to 0.99; unadjusted data: HR = 0.84, 95% CI = 0.69 to 1.02). CONCLUSIONS: Erythropoietin treatment may reduce the risk for blood transfusions and improve hematologic response in cancer patients. However, our favorable survival outcome is in contrast to two large (N = 351 and 939) recently published randomized controlled trials in which erythropoietin-treated patients had statistically significantly worse survival than untreated patients. Possible reasons for the disparity with our results include differences in study population and design, higher target hemoglobin levels and higher risk of thromboembolic complications, and concerns that erythropoietin may stimulate tumor growth.

Anemia↗
PubMed2005

Effectiveness of erythropoietin in the treatment of patients with malignancies: methods and preliminary results of a Cochrane review.

Cancer and cancer therapy-associated anemia may have an impact on tumor response and overall survival. Additionally, anemia represents an important economic factor. Therefore, therapeutic alternatives such as erythropoietin (EPO) and red blood cell transfusions have to be evaluated systematically. The effectiveness of recombinant human EPO to prevent or alleviate anemia in patients with malignant disease was determined. Randomized controlled trials comparing prophylaxis or treatment of anemia with EPO plus red blood cell transfusion (RBCT) or RBCT only in patients with malignant disease undergoing antineoplastic therapy were included. The endpoints needed for RBCT were hematological response (hemoglobin increase of 2g/dL or hematocrit increase of 6%), tumor response, and overall survival. Medical databases (Cochrane Library, MEDLINE, EMBASE) and conference proceedings were searched (1985-2001). Full-text and abstract publications were included as well as unpublished data. Data extraction and quality assessment were done in duplicate. All authors were contacted to obtain missing data. Out of 33 eligible studies, 27 trials with 3,287 randomized patients were included.

Anemia↗
PubMed2004

No evidence for an impact of selenium supplementation on environment associated health disorders--a systematic review.

In addition to vitamin C (and other vitamins/antioxidants), clinical ecologists (functional medicine) recommend selenium supplementation as a fundamental therapeutic remedy for the treatment of environment associated health disorders. This recommendation is based on the postulation that the trace element selenium inhibits oxidative stress generated during endogenous detoxification of xenobiotics (phase 1) by increasing selenium-dependent glutathione peroxidase activity, and that it counteracts heavy metal toxicity by forming inert metal complexes. The objective of this review was to investigate whether there are any valid studies providing reliable evidence of the therapeutic benefits of selenium supplementation in potentially environment associated health disorders. A systematic review was conducted based on the rigorous and well-defined methods developed by the Cochrane Collaboration. To achieve the demanding standards for systematic review set by the Cochrane Collaboration, study selection, quality assessment and data abstraction were performed independently and in duplicate using a standardized protocol. Overall, 1290 studies were identified as being eligible for inclusion. Twelve of these met the inclusion criteria and their quality was evaluated individually. None of the studies included in the analysis provided evidence of the therapeutic benefits of selenium supplementation in environment associated health disorders.

Aged↗
PubMed2003

Impact of granulocyte colony-stimulating factor (CSF) and granulocyte-macrophage CSF in patients with malignant lymphoma: a systematic review.

The granulopoiesis-stimulating factors, granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF), are used to prevent neutropenia and febrile neutropenia in patients with malignant lymphoma. The question as to whether G-CSF/GM-CSF improves dose-intensity, tumour response and overall survival (OS) has not yet been answered. As the results from single studies are inconclusive, a systematic review was performed to determine the effectiveness of G-CSF/GM-CSF. Randomized controlled trials comparing prophylaxis with G-CSF/GM-CSF versus no prophylaxis in adult patients with malignant lymphoma undergoing conventional chemotherapy were included. Medical databases (Cochrane Library, Medline, Embase) and conference proceedings were searched. All authors were contacted to obtain missing data. We included 11 studies making a total of 1434 patients. Compared with no prophylaxis, G-CSF/GM-CSF significantly reduced the relative risk (RR) for neutropenia [RR 0.64 [95% confidence interval (CI) 0.55-0.75]] febrile neutropenia (RR 0.74 [95% CI 0.62-0.89]) and infection (RR 0.74 [95% CI 0.64-0.85]). G-CSF/GM-CSF did not decrease infection-related mortality (RR 2.07 [95% CI 0.81-5.34]), improve complete remission (CR) (RR 1.06 [95% CI 0.96-1.16]) or OS (HR 0.98 [95% CI 0.81-1.18]). In conclusion, G-CSF/GM-CSF given during conventional chemotherapy in malignant lymphoma patients reduced the RR of neutropenia, febrile neutropenia and infection. However, there is no evidence that G-CSF/GM-CSF improved CR and OS in this clinical setting.

Adult↗
PubMed2002

Inflation of type I error rate in two statistical tests for the detection of publication bias in meta-analyses with binary outcomes.

The use of meta-analysis to combine results of several trials is still increasing in the medical field. The validity of a meta-analysis may be affected by various sources of bias (for example, publication bias, language bias). Therefore, an analysis of bias should be an integral part of any systematic review. Statistical tests and graphical methods have been developed for this purpose. In this paper, two statistical tests for the detection of bias in meta-analysis were investigated in a simulation study. Binary outcome data, which are very common in medical applications, were considered and relative effect measures (odds ratios, relative risk) were used for pooling. Sample sizes were generated according to findings in a survey of eight German medical journals. Simulation results indicate an inflation of type I error rates for both tests when the data are sparse. Results get worse with increasing treatment effect and number of trials combined. Valid statistical tests for the detection of bias in meta-analysis with sparse data need to be developed.

Computer Simulation↗
PubMed2002

Artificial neural networks for diagnosis and prognosis in prostate cancer.

The application of artificial neural networks (ANNs), especially feed-forward neural networks (FFNNs), has become very popular for diagnosis and prognosis in clinical medicine, often accompanied by exaggerated statements of their potential. The excitement stems mainly from the fact that ANNs were developed as attempts to model the decision process of the human brain. Traditionally, logistic regression models and proportional hazard regression models have been used in these applications. In this article, FFNNs are introduced as flexible, nonlinear regression models and necessary precautions for their use are discussed. Furthermore, the results of a literature survey of applications of ANNs in prostate cancer published between 1999 and 2001 are described; most applications suffer from methodologic deficiencies. It is concluded that there is so far no evidence that the application of ANNs provide real progress in the field of diagnosis and prognosis in prostate cancer.

Diagnostic Techniques and Procedures↗
PubMed2002

Ceftriaxone versus other cephalosporins for perioperative antibiotic prophylaxis: a meta-analysis of 43 randomized controlled trials.

The efficacy of ceftriaxone versus other cephalosporins in the perioperative prophylaxis of surgical wound, urinary tract and respiratory tract infections was compared in a meta-analysis of randomized controlled trials published between 1986 and 1996, identified from the Medline, Embase, SIGLE, ROPU, DHSS-Data and Medikat Cologne databases. Studies were grouped by type of infection, operative specialty, wound classification, study quality and other factors, and assessed for relative risk (RR). Forty-three studies with a total of 13,482 patients met our inclusion criteria. RR for surgical wound infection (n = 13,303 patients) was 30% lower in the ceftriaxone versus control groups [98.3% confidence interval (CI): 0.55-0.89; p = 0.0002]. In urinary tract infections (n = 8,865 patients), the primary analysis of all studies showed marked superiority for ceftriaxone (RR: 0.53; 98.3% CI: 0.43-0.67) but not in studies with CDC-defined infections (RR: 0.63; 98.3% CI: 0.36-1.12). In both types of infection, ceftriaxone was superior in contaminated operations. The data showed no advantage for ceftriaxone in other operations. In respiratory tract infections (n = 9,567 patients), there was no significant difference: the RR was 0.81 (98.3% CI: 0.61-1.09; p = 0.04).

Antibiotic Prophylaxis↗