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PubMed2006

Bayesian methods for evidence synthesis in cost-effectiveness analysis.

Recently, health systems internationally have begun to use cost-effectiveness research as formal inputs into decisions about which interventions and programmes should be funded from collective resources. This process has raised some important methodological questions for this area of research. This paper considers one set of issues related to the synthesis of effectiveness evidence for use in decision-analytic cost-effectiveness (CE) models, namely the need for the synthesis of all sources of available evidence, although these may not 'fit neatly' into a CE model. Commonly encountered problems include the absence of head-to-head trial evidence comparing all options under comparison, the presence of multiple endpoints from trials and different follow-up periods. Full evidence synthesis for CE analysis also needs to consider treatment effects between patient subpopulations and the use of nonrandomised evidence. Bayesian statistical methods represent a valuable set of analytical tools to utilise indirect evidence and can make a powerful contribution to the decision-analytic approach to CE analysis. This paper provides a worked example and a general overview of these methods with particular emphasis on their use in economic evaluation.

Bayes Theorem↗
PubMed2005

Reformulating and simplifying the DF analysis model.

DeFries-Fulker (DF) Analysis for unselected populations is reformulated as a no-intercept model with centered variables and only two independent variables. The reformulation serves three purposes. First, the original formulation implicitly estimated two different values for c2 and two values for h2. The new formulation resolves this ambiguity. Second, because the original formulation estimated h2 with the coefficient from a regression-interaction term, whether to center the interaction variables was unclear. The new formulation explicitly resolves this issue. Finally, the new formulation estimates fewer parameters, and therefore improves estimation efficiency and statistical power.

Fertility↗
PubMed1999

Bleeding complications with enoxaparin for deep venous thrombosis prophylaxis.

The safest and most efficacious method of deep venous thrombosis prophylaxis remains controversial. With the use of enoxaparin, a low-molecular-weight heparin, becoming ubiquitous in many institutions, we specifically examined bleeding complications related to its use. A case-control study was conducted on consecutive patients receiving enoxaparin prophylaxis after primary or revision total knee or total hip arthroplasty or hip hemiarthroplasty. Matched controls receiving no pharmacologic anticoagulation were identified. Patient and operative characteristics, hematologic values, and timing of enoxaparin dosing were analyzed as related to major and minor bleeding complications. A total of 152 procedures with enoxaparin and an equal number of control cases were included for a total of 304 patients. The enoxaparin group had a 23.7% total complication rate compared to 16.5% for the control group (P = .11). The power of the test was .35 and indicated that approximately 970 patients would need to be reviewed to have at least an 80% chance of finding a statistically significant difference. Major complications occurred in 5 patients (3.3%) in the enoxaparin group and 2 (1.3%) in the control group (P = .25, power = .21). Minor complications in the enoxaparin group were slightly higher but not significant at 20.4% versus 15.1% in the control group (P = .23). There were significantly fewer minor complications in the enoxaparin group after primary single-joint procedures (16.50%) than all other procedures (32.4%). Patients receiving the first dose of enoxaparin 10 hours or more postoperatively had significantly fewer complications (P = .05). The postoperative hematocrit drop was significantly greater for the enoxaparin group for all procedures (P = .003) as well as for primary single procedures (P = .0005). The postoperative transfusion requirement was significantly greater after primary single procedures (P = .02) in the enoxaparin group. One patient with an epidural catheter and receiving enoxaparin postoperatively developed an epidural hematoma. Although there were not significantly more complications with enoxaparin, there was evidence of significantly increased postoperative bleeding. The low-power analysis reveals that a large number of patients (970-1,700) are required to show a statistically significant difference in bleeding complications between the 2 groups. To minimize complications, a short period to allow initial hemiostasis postoperatively is recommended, as is preferential use of enoxaparin for primary single-joint replacements. Enoxaparin used in conjunction with an indwelling epidural catheter is not recommended.

Aged↗
PubMed2005

Cytokine gene polymorphisms and acute liver graft rejection: a meta-analysis.

In the field of liver transplantation, 7 reports have been published investigating the association between polymorphisms in cytokine genes and the occurrence of acute rejection in liver graft recipients. However, most of the individual studies lack the statistical power to detect a small-to-moderate effect of cytokine gene polymorphisms on the acute rejection rate. To overcome this problem, we performed a quantitative meta-analysis of 7 gene-association studies that were comparable with regard to definition of acute rejection and the type of immunosuppression used. In the overall analysis, the interleukin (IL)-10 polymorphism at position -1082 was identified as a genetic risk factor for acute liver graft rejection; liver transplant recipients carrying the IL-10 -1082.A allele displayed a lower rejection rate (common odds ratio [OR], .6; 95% confidence interval [CI], .4-.9). For the tumor necrosis factor (TNF)-A -308 polymorphism, a common OR could not be calculated due to significant heterogeneity of ORs between the studies (mean OR, 1.4; 95% CI, .8-2.6). No associations were found between acute liver graft rejection and single nucleotide polymorphisms in the IL-6 (position -174) and transforming growth factor (TGF)-beta1 (positions +869 and +915) genes. In conclusion, results from this meta-analysis suggest a role for the IL-10 -1082 polymorphism in human liver graft rejection.

Acute Disease↗
PubMed2004

Relative extrinsic stain removal effectiveness of a new battery-powered toothbrush and a flat trim manual toothbrush.

PURPOSE: To evaluate the stain removal efficacy of two different toothbrush designs using a laboratory stained pellicle test with seven different dentifrices. METHODS: The toothbrushes were a prototype powered toothbrush (Crest SpinBrush Pro Whitening) and an ADA reference manual toothbrush, as a control. The dentifrices used in the study were: Crest Dual Action Whitening (Cool Mint), Crest Extra Whitening with Tartar Control (Clean Mint), Crest MultiCare Whitening (Fresh Mint), Colgate Total, Colgate Total Plus Whitening, Arm & Hammer Advance White with Tartar Control and Rembrandt Plus with Active Dental Peroxide. This was a randomized, parallel group study that examined stain removal with a novel toothbrushing configuration adapted for powered and manual toothbrushes. Stain was scored before and after brushing for two consecutive, 1-minute periods using digital image analysis. The mean change in L* was statistically compared between toothbrushes with ANCOVA. Labial enamel specimens were obtained from bovine permanent incisors and these specimens were subjected to a laboratory staining process until the L* values for the samples were in the range of 35-45. Digital images for CIE L*a*b* analysis were captured using a high-resolution digital camera under standard polarized lighting conditions. Based on the L* values, the enamel specimens were divided into 14 groups of nine specimens each. RESULTS: Baseline L* values ranged from 40.62 to 41.38 for the 14 toothbrush/dentifrice combinations. The change in L* (post-brushing minus baseline), denoted as deltaL*, was calculated for each specimen and the resulting data were subjected to a two-way ANCOVA. Toothbrush type and dentifrice type were the two terms in the model, and baseline L* was the covariate. Pairwise tests were performed on the adjusted means in order to compare the stain removal efficacy of the two toothbrushes for each of the seven dentifrices evaluated. The powered toothbrush resulted in statistically significantly greater deltaL* values (all P < or = 0.006) than the manual toothbrush for every dentifrice tested. The deltaL* values for dentifrices used with the powered toothbrush were from 66.0-164.2% higher than for the same dentifrice used with the manual toothbrush.

Analysis of Variance↗
PubMed1991

Identification of first acute Q wave and non-Q wave myocardial infarction by multivariate analysis of body surface potential maps.

BACKGROUND: Patients with acute non-Q wave myocardial infarction (NQMI) appear to have more jeopardized residual myocardium at high risk for subsequent angina, reinfarction, or malignant arrhythmias than patients with acute Q wave myocardial infarction (QMI). Unfortunately, conventional electrocardiographic (ECG) criteria have limited utility in recognizing NQMI. METHODS AND RESULTS: The present study combines the increased information content of body surface potential maps (BSPM) over the 12-lead ECG with the power of multivariate statistical procedures to identify a practical subset of leads that would allow improved diagnosis of NQMI. Discriminant analysis was performed on 120-lead data recorded simultaneously in 159 normal subjects and 308 patients with various types of myocardial infarction (MI) by using instantaneous voltages on time-normalized P, PR, QRS, and ST-T waveforms as well as the duration of these waveforms as features. Leads and features for optimal separation of 159 normals from 183 patients with recent or old QMI (group A) were selected. A total of six features from six torso sites accounted for a specificity of 96% and a sensitivity of 94%. All lead positions were outside the conventional electrode sites and selected features were voltages at mid-P, early and mid-QRS, and before and after the peak of the T wave. The discriminant function was then tested on 57 patients with acute NQMI (group B) and 68 patients with acute QMI (group C): Rates of correct classification were 91% and 93%, respectively. Because of the possible deterioration of the results caused by ST-T abnormalities also present in other clinical entities, a second classification model including an independent group of 116 patients with left ventricular hypertrophy (LVH) but without MI was developed. Two additional measurements were required, namely, P wave duration and a mid-QRS voltage on a lead located 10 cm below V1. Testing the model on both acute MI groups produced correct classification rates of 88% for acute NQMI and 93% for acute QMI. Group mean BSPM were plotted for the three MI groups at successive instants throughout the PQRST waveform. Typical patterns for each MI group were identified during PQRST by removing the corresponding normal variability at each electrode site from sequential MI maps. These standardized maps or discriminant maps provided information on the capability of each measurement at each electrode site and at each instant to separate each class of MI from the normal group (N). Striking similarities were observed between the three MI groups, particularly at mid-QRS and throughout ST-T. The closest resemblance was between acute NQMI and old QMI. Discriminant analysis was also performed on the 12-lead ECG: The first classification model (N versus MI) produced correct classification rates of 85% for acute QMI and 70% for NQMI. With the second model (MI versus N or LVH), correct rates were 81% and 65%, respectively. CONCLUSIONS: Diagnosis of acute NQMI and QMI (also in the presence of LVH) can be improved substantially by appropriate selection of ECG leads and features. Comparison of discriminant maps from groups A, B, and C does not support the concept of acute NQMI as a distinct ECG entity but rather as a group with infarcts of smaller size. However, pathophysiological and clinical differences between acute NQMI and acute QMI influence long-term risks and may define different therapeutic approaches.

Adult↗
PubMed1991

Risk factors for Alzheimer's disease: overview of the EURODEM collaborative re-analysis of case-control studies. EURODEM Risk Factors Research Group.

Studies of risk factors for Alzheimer's disease have been hampered by low statistical power. The data from 11 case-control studies were pooled and re-analysed to evaluate the evidence for the association of Alzheimer's disease with family history of dementia and related disorders, parental age, medical history, and environmental factors. This paper gives a brief description of the participating studies and discusses the strategy that has been followed in the collaborative analysis.

Adult↗
PubMed1999

Heart rate variability in healthy volunteers during normobaric and hyperbaric hyperoxia.

Inhaled supranormal partial pressure of oxygen induces bradycardia and peripheral vasoconstriction. The exact mechanism of the decreasing heart rate is not clear, but the autonomic nervous system is partly involved. In the present study the role of the autonomic nervous system in hyperoxic bradycardia was evaluated by using the power spectral analysis of heart rate variability. Ten healthy volunteers participated in four experiments: (i) hyperbaric oxygen treatment (100% oxygen at 2.5 ATA), (ii) hyperbaric air treatment (O2 21% at 2.5 ATA), (iii) oxygen treatment at normal pressure (100% O2, 1 ATA) and (iv) air breathing at normal pressure (21% O2, 1 ATA). During the experiments, ECG was registered and subjected to power spectral analysis. The volunteers rated their perception of temperature, ear discomfort, sweating and excitement on a visual analogue scale. Statistical comparison of the results of the four trials was conducted with a two-way ANOVA for repeated measurements. Heart rate decreased during all interventions, but there were no statistically significant differences between the sessions. High frequency variability of heart rate variability and Hayano's index of HF power increased and LF/HF ratio decreased with increasing partial pressure of oxygen. Our results suggest, that normobaric and hyperbaric hyperoxia increase parasympathetic influence in the regulation of the heart.

Adult↗
PubMed2001

A genomewide screen for autism susceptibility loci.

We report the analysis of 335 microsatellite markers genotyped in 110 multiplex families with autism. All families include at least two "affected" siblings, at least one of whom has autism; the remaining affected sibs carry diagnoses of either Asperger syndrome or pervasive developmental disorder. Affected sib-pair analysis yielded multipoint maximum LOD scores (MLS) that reach the accepted threshold for suggestive linkage on chromosomes 5, X, and 19. Nominal evidence for linkage (point-wise P<.05) was obtained on chromosomes 2, 3, 4, 8, 10, 11, 12, 15, 16, 18, and 20, and secondary loci were found on chromosomes 5 and 19. Analysis of families sharing alleles at the putative X chromosomal linked locus and one or more other putative linked loci produced an MLS of 3.56 for the DXS470-D19S174 marker combination. In an effort to increase power to detect linkage, scan statistics were used to evaluate the significance of peak LOD scores based on statistical evidence at adjacent marker loci. This analysis yielded impressive evidence for linkage to autism and autism-spectrum disorders with significant genomewide P values <.05 for markers on chromosomes 5 and 8 and with suggestive linkage evidence for a marker on chromosome 19.

Asperger Syndrome↗
PubMed1996

Robustness and power of analysis of covariance applied to data distorted from normality by floor effects: homogeneous regression slopes.

We investigate through computer simulations the robustness and power of two group analysis of covariance test applied to small samples distorted normality by floor effects when the regression slopes are homogeneous. We consider four parametric analysis of covariance tests that vary according to the treatment of the homogeneity of regression slopes and two t-tests on unadjusted means and on difference scores. Under the null hypothesis of no difference in means, we estimated actual significance levels by comparing observed test statistics to appropriate values from the F and t distributions for nominal significance levels of 0.10, 0.05, 0.02 and 0.01. We estimated power by similar comparisons under various alternative hypothesis. The hierarchical approach (that adjusts for non-homogeneous slopes if found significant), the test that assumes homogeneous regression slopes, and the test that estimates separate regression slopes in each treatment were robust. In general, each test produced power at least equal to that expected from normal theory. The textbook approach, which does not test for mean differences when there is significant non-homogeneity, was conservative but also had good power. The t-tests were robust but had poorer power properties than the above procedures.

Analysis of Variance↗
PubMed2004

Principal component analysis is a powerful instrument in occupational hygiene inquiries.

Several investigators have successfully used principal component analysis (PCA) in interpreting occupational hygiene data. However, traditional textbooks in occupational hygiene provide no guidance for the application and interpretation of PCA. In this article I briefly review the basics of PCA (for those not statistically inclined), provide some guidelines for performing PCA (and designing studies that use the power of PCA), illustrate its application in understanding exposure to mixtures and the characterization of 'peak exposure', and highlight other benefits that occupational hygienists stand to gain by including PCA in their 'statistical toolkit'. I hope that this article will promote greater use and understanding of a data analysis approach that has long been helping investigators outside the field of occupational hygiene to unravel the structure behind the complex relationships among multiple correlated variables.

Humans↗
PubMed1999

Hypothesis testing under mixture models: application to genetic linkage analysis.

In this paper we propose a new class of statistics to test a simple hypothesis against a family of alternatives characterized by a mixture model. Unlike the likelihood ratio statistic, whose large sample distribution is still unknown in this situation, these new statistics have a simple asymptotic distribution to which to refer under the null hypothesis. Simulation results suggest that it has adequate power in detecting the alternatives. Its application to genetic linkage analysis in the presence of the genetic heterogeneity that motivated this work is emphasized.

Biometry↗
PubMed1997

Learning and understanding the Kruskal-Wallis one-way analysis-of-variance-by-ranks test for differences among three or more independent groups.

When several treatment methods are available for the same problem, many clinicians are faced with the task of deciding which treatment to use. Many clinicians may have conducted informal "mini-experiments" on their own to determine which treatment is best suited for the problem. These results are usually not documented or reported in a formal manner because many clinicians feel that they are "statistically challenged." Another reason may be because clinicians do not feel they have controlled enough test conditions to warrant analysis. In this update, a statistic is described that does not involve complicated statistical assumptions, making it a simple and easy-to-use statistical method. This update examines the use of two statistics and does not deal with other issues that could affect clinical research such as issues affecting credibility. For readers who want a more in-depth examination of this topic, references have been provided. The Kruskal-Wallis one-way analysis-of-variance-by-ranks test (or H test) is used to determine whether three or more independent groups are the same or different on some variable of interest when an ordinal level of data or an interval or ratio level of data is available. A hypothetical example will be presented to explain when and how to use this statistic, how to interpret results using the statistic, the advantages and disadvantages of the statistic, and what to look for in a written report. This hypothetical example will involve the use of ratio data to demonstrate how to choose between using the nonparametric H test and the more powerful parametric F test.

Analysis of Variance↗
PubMed2005

[Analysis of motor performance status in students of Han nationality in fifteen provinces in China].

OBJECTIVE: To analyze the motor performance status in students of Han nationality in fifteen provinces in china. METHODS: Totally, 161 804 students of Han nationality aged from 7 to 18 years old were involved in the Chinese Surveillance on Students' Physical Fitness and Health in 2004. Motor abilities were accessed with the aid of gripping power, 50 m dash, standing long jump, and 1-min sit-ups. Based on general statistical description, principal component analysis and linear regression, the development characters of students' motor performance were explored. RESULTS: This research showed some characters similar to those of last ones: motor capability was improved in correlation with age; boys did better than girls, the difference between 18 year-old rural boys and rural girls was 15.3 kg, -2.0 s, 58.6 cm, 8.7/min; the urban students performed better than the rural ones, the difference between 15 year-old urban boys and rural boys was 0.9 kg, -0.2 s, 3.5 cm, 3.5/min. The first principal component might represent the 4 tests greatly. Regression analysis on principal component quantitatively interpreted the influence of factors such as age, sex and area. CONCLUSIONS: The general principles of exercise quality development of students are still in work. Principal component analysis should be adequate and convenient in motor performance analysis.

Adolescent↗
PubMed2000

Detection of Neisseria gonorrhoeae and Chlamydia trachomatis colonization of the gravid cervix.

OBJECTIVES: The aims of the study were to determine whether a Gram stain of cervical mucus can accurately rule out infection with Neisseria gonorrhoeae or Chlamydia trachomatis and to compare a diagnostic test that is based on the polymerase chain reaction with a deoxyribonucleic acid probe in the detection of these organisms. STUDY DESIGN: Gravid patients were screened for N gonorrhoeae and C trachomatis with a deoxyribonucleic acid probe, Gram stain, and analysis with the polymerase chain reaction. A normal, noninfected sample was defined by <10 polymorphonuclear leukocytes per high-power field on the Gram stain. Standard statistical methods were used to compare results of the Gram stain and the deoxyribonucleic acid probe, as well as to compare results of deoxyribonucleic acid probe hybridization and polymerase chain reaction analysis. A P value of <.05 was considered statistically significant. RESULTS: Patient enrollment totaled 519. The prevalence of infection as determined by deoxyribonucleic acid probe hybridization was 1.4% for N gonorrhoeae (7/518) and 6.8% for C trachomatis (35/518). The cervical Gram stain predicted the absence of infection in 17% (90/518) of patients, with a negative predictive value of 99% for N gonorrhoeae and 97% for C trachomatis. African American race, age <20 years, and unmarried status were all predictors of the presence of C trachomatis or N gonorrhoeae cervicitis. For the patients who lacked these risk factors (n = 74), the Gram stain had 100% negative predictive value. Analysis with the polymerase chain reaction detected 8 additional patients with C trachomatis and 105 additional patients with N gonorrhoeae, in comparison with deoxyribonucleic acid probe hybridization. CONCLUSION: The cervical Gram stain can accurately predict the absence of N gonorrhoeae and C trachomatis in gravid women. Analysis with the polymerase chain reaction indicates that N gonorrhoeae and C trachomatis are significantly more prevalent in this population than previously reported.

Cervix Uteri↗
PubMed2005

Modelling of the shielding capabilities of the existing solid radioactive waste storages at Ignalina NPP.

There is only one nuclear power plant in Lithuania--Ignalina NPP (INPP). The INPP operates two similar units with design electrical power of 1500 MW. The units were commissioned in 1983 and 1987 respectively. From the beginning of the INPP operation all generated solid radioactive waste was collected and stored at the Soviet type solid radwaste facility located at INPP site. The INPP solid radwaste storage facility consists of four buildings, namely building No. 155, No. 155/1, No. 157 and No. 157/1. The buildings of the INPP solid radwaste storage facility are reinforced concrete structures above ground. State Nuclear Safety Inspectorate (VATESI) has specified that particular safety analysis must be performed for existing radioactive waste storage facilities of the INPP. As part of the safety analysis, shielding capabilities of the walls and roofs of these buildings were analysed. This paper presents radiation shielding analysis of the buildings No. 157 and No. 157/1 that are still in operation. The buildings No. 155 and No. 155/1 are already filled up with the waste and no additional waste loading is expected.

Computer Simulation↗
PubMed1990

Correlations of acoustic tissue typing of malignant melanoma and histopathologic features as a predictor of death.

Forty-six eyes with uveal melanoma were scanned with a computerized diagnostic ultrasound system before enucleation, and light microscope sections were obtained. Tumors were characterized by ultrasonically measured dimensions and power spectrum analysis, which provided information not available in conventional A- or B-scan ultrasonography. Histopathologic features, including cell clustering pattern, cell type, pigmentation, vascularity, and necrosis, were quantified. Statistically significant correlations were found between parameters derived from the power spectrum and histologic characteristics. Patients were followed up for up to ten years with 14 deaths occurring because of metastases. Using a Cox relative risk model with histopathologic data, a risk model comprising pigmentation and cell type (P less than .0001) was obtained. Using ultrasonic characteristics, a model comprising tumor volume and scatterer concentration (P = .0062) was obtained. The results suggest that ultrasonic tissue characterization and three-dimensional biometry may provide improved in vivo prognostic indicators for uveal melanoma.

Eye Enucleation↗