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Meta-Analysis
Published in Trevor F. Cox, Medical Statistics for Cancer Studies, 2022
The z-value for testing is with , and hence the evidence suggests that preoperative chemotherapy is a benefit for survival. The combined estimate is shown on the forest plot as a horizontally stretched diamond, the centre being placed at the value of HR and the left and right hand ends at the lower and upper points of the confidence interval. Here, the confidence interval is rather short and so the diamond here is not particularly stretched.
Genomic Biomarker Clinical Trial Designs
Published in Susan Halabi, Stefan Michiels, Textbook of Clinical Trials in Oncology, 2019
At the final analysis, a single significance test is performed comparing the test treatment to control. It includes all randomized patients but has the specific form described in the following way. Let Zj denote the z value for comparing the test treatment to control for patients accrued during period j. If there is a single interim analysis, then j = 1 or 2. If there are two interim analyses, then j = 1, 2, or 3. We assume that Z is normalized to have a null distribution that is approximately normal with mean 0 and variance 1. The single statistical significance test conducted is based on the test statistic where the weights are pre-specified, non-negative, and add up to 1. Under the null hypothesis, this statistic should be approximately normal with mean 0 and variance 1.
Human Noroviruses
Published in Dongyou Liu, Handbook of Foodborne Diseases, 2018
G. Sanchez, W. Randazzo, D.H. D'Souza
It is crucial to first understand the thermal resistance and properties of a target pathogen in order to design effective thermal treatment processes for their inactivation and control. The thermal behavior of pathogens is determined using the D-value which is defined as the time at a given temperature to cause a 1-log reduction of the target.91 In addition, z-values are also determined, which is universally defined as the change in the temperature required to cause a change in the D-value by 1-log (or a 10-fold change in D-value). The z-value represents the temperature required for the thermal destruction curve to change by 1-log cycle, and the z-value for a given microorganism should not change when tested under the varying conditions, such as various food matrices or buffer types.91 These values are determined for the individual targets in various food commodities to ensure proper heating and processing for food safety and to prevent outbreaks, recalls and food losses. A detailed literature review on the heat inactivation kinetics of human enteric viruses, including HNoV surrogates, is provided by Bozkurt et al.91 Some of the findings are summarized as follows.
Reference change value and measurement uncertainty in the evaluation of tumor markers
Published in Scandinavian Journal of Clinical and Laboratory Investigation, 2021
Hatice Bozkurt Yavuz, Mehmet Akif Bildirici, Hüseyin Yaman, Süleyman Caner Karahan, Yüksel Aliyazıcıoğlu, Asım Örem
The Z value in the formula is the measure of the standard deviation (SD) suitable for the desired confidence interval. In most of the studies on analytical and biological components of variation, RCV calculations are made and the Z value is generally used as 1.96 at 95% confidence interval and 2.58 at 99% confidence interval. But it should not be forgotten that these Z values are suitable for two-way evaluations and express both increase and decrease. In clinical decision management, one-way Z values should be used, since only a significant increase or decrease in test results will be evaluated [4]. Therefore, based on the recommendation of Cooper et al., since it is more appropriate to use one-way change, Z values are taken as 1.65 at 95% confidence interval and 2.33 at 99% confidence interval [5]. Likewise, Fraser stated that one-way Z values should be used when evaluating the result of the analyte measured in clinical decision management since there may be either a significant increase or a significant decrease [4].
SPISE and other fasting indexes of insulin resistance: risks of coronary heart disease or type 2 diabetes. Comparative cross-sectional and longitudinal aspects
Published in Upsala Journal of Medical Sciences, 2019
Jan Cederholm, Björn Zethelius
Cox regression analysis was used to estimate hazard ratios (HR) with the four fasting resistance indexes as predictors of long-term fatal or non-fatal CHD as outcome (Table 3). HR with 95% confidence intervals (CI) were given per 1 SD increase of each predictor index, allowing for a direct comparison between the strengths of the four hazard ratios. The Z statistic with its p values also indicates the association between predictor and outcome – the higher Z value, the stronger association. Covariance adjustment was performed with several important conventional cardiovascular risk factors and clinical characteristics: systolic blood pressure, smoking, cystatin C, albuminuria, Charlson comorbidity index, and a history of CHD. The proportional hazards assumption at Cox regression was confirmed with scaled Schoenfeld residuals, estimated with the R statistical package cox.zph. The likelihood ratio (LR) test indicates global model fit – the higher value, the better fit. Harrell’s C (concordance) measures discrimination between those who will have and those who will not have events – the higher value, the better discrimination, estimated with the R statistical package dynpred.
Breast Cancer Association with Cytomegalo Virus—A Tertiary Center Case-Control Study
Published in Journal of Investigative Surgery, 2019
Anilkumar Surendran, Meer M. Chisthi
When the Mann–Whitney U-test was applied to the IgG levels, the value of U was 1786. The distribution was approximately normal and hence, the Z-value was used. The Z-Score was 0.30617 and the P value was 0.76. The result was not significant at P < 0.05. On applying the Mann-Whitney U test to the IgM levels, the value of U was 1674. The distribution was approximately normal again and hence, the Z-value was used. The Z-Score was 0.30617 and the P value was 0.76. The result was not significant at P < 0.05. When the unpaired Student's t test was applied to the IgG values, the two-tailed P value was found to equal 0.82. This difference was not significant. On applying the unpaired Student's t-test to the IgM values, the two-tailed p value was found to equal 0.45. This difference was also not significant. The sensitivity of IgG to CMV in relation to breast cancer was found to be 1 and specificity was calculated to 0. In the case of IgM to CMV the values of sensitivity and specificity were found to be 0 and 1, respectively.