Wilcoxon test

The output data set pvalue contains numerous Wilcoxon test statistics. Assuming that you want the two-sided normal approximation test p-value, the variable in the pvalue data set that you want is called P2 WIL. ... 

The acceptance criterion for recovery data is 98-102% or 95-105% for drug preparations. In biological samples, the recovery should be 10%, and the range of the investigated concentrations is 20% of the target concentrations. For trace level analysis, the acceptance criteria are 70-120% (for below 1 ppm), 80-120% (for above 100 ppb), and 60-100% (for below 100 ppb) [2]. For impurities, the acceptance criteria are 20% (for impurity levels <0.5%) and 10% (for impurity levels >0.5%) [30], The AOAC (cited in Ref. [11]) described the recovery acceptance criteria at different concentrations, as detailed in Table 2. A statistically valid test, such as a /-test, the Doerffel-test, or the Wilcoxon-test, can be used to prove whether there is no significant difference between the result of accuracy study with the true value [29],... 

The Wilcoxon Rank-Sum Test could be used to analyze the event times in the absence of censoring. A Generalized Wilcoxon Test, sometimes called the Gehan Test, based on an approximate chi-square distribution, has been developed for use in the presence of censored observations. 

Both the Log-Rank and the Generalized Wilcoxon Tests are nonparametric tests, and require no assumptions regarding the distribution of event times. When the event rate is greater early in the trial than toward the end, the Generalized Wilcoxon Test is the more appropriate test since it gives greater weight to the earlier differences. 

Statistical Analysis. Analysis of variance (ANOVA) of toxicity data was conducted using SAS/STAT software (version 8.2 SAS Institute, Cary, NC). All toxicity data were transformed (square root, log, or rank) before ANOVA. Comparisons among multiple treatment means were made by Fisher s LSD procedure, and differences between individual treatments and controls were determined by one-tailed Dunnett s or Wilcoxon tests. Statements of statistical significance refer to a probability of type 1 error of 5% or less (p s 0.05). Median lethal concentrations (LCjq) were determined by the Trimmed Spearman-Karber method using TOXSTAT software (version 3.5 Lincoln Software Associates, Bisbee, AZ). 

In the next section we will discuss Kaplan-Meier curves, which are used both to display the data and also to enable the calculation of summary statistics. We will then cover the logrank and Gehan-Wilcoxon tests which are simple two group comparisons for censored survival data (akin to the unpaired t-test), and then extend these ideas to incorporate centre effects and also allow the inclusion of baseline covariates. 

The Kaplan-Meier curves do not of themselves provide a formal, p-value, comparison of the treatments. This comparison of the survival curves is undertaken using either the logrank test or the Gehan-Wilcoxon test. We will look at these two test procedures in turn. 

Verapamil and its active metabolite norverapamil were assayed from serum (frozen at -18°C) using a gas chromatographic-mass spectrometric method [5]. The detection limit of the method was 1 ng/ml. The areas under the concentration-time curves (AUC 0-32 h) were calculated by the trapezoidal method. Statistical evaluation was carried out using the paired Wilcoxon test and paired Student s t test. 

Table I. Critical Probabilities (3 ) for the Evolution of Mutagenicity with Ozonation (Wilcoxon Test Analysis on TA98 Data)...

GAC and Ozone-GAC. The Wilcoxon test was applied to compare results before and after GAC filtration. By using data for DCM or MeOH extracts, no interpretation of the variations observed and no statistical conclusions can be drawn. This situation is true for GAC treatment alone and for all combinations of dose, contact time, and GAC (Table III). 

Disinfection with Chlorine and Chlorine Dioxide. The comparison of the mutagenic activity of the DCM extract before and after disinfection treatment was studied by the Wilcoxon test. No statistical conclusions on disinfection effects can be drawn. However, the MeOH extract showed a significant decrease in mutagenic activity for the line 2 chlorine treatment. Comparison of the two disinfection treatments for the nonozonated GAC filtered water (treatment line 4) shows that chlorine disinfection yields greater mutagenic activity of the DCM extract than chlorine dioxide (Table V). 

Complete Treatment Line. The Wilcoxon test was applied to compare mutagenic activity before RSF and after complete treatment lines. Treatment line 4 with chlorine dioxide disinfection significantly decreased the mutagenic activity of the DCM extract. No other statistically significant differences were observed for any other treatment lines from data on DCM or MeOH extracts (Table VI). 

All data were analyzed as paired samples using the Wilcoxon test. For all calculations, SPSS software was used. 

The Wilcoxon s Rank-Sum Test (WRST) is a non-parametric alternative. The WRST is robust to the normal distribution assumption, but not to the assumption of equal variance. Furthermore, this test requires that the two groups of data under comparison have similarly shaped distributions. Non-parametric tests typically suffer from having less statistical power than their parametric counterparts. Similar to the /-test, the WRST will exhibit false positive rate inflation across a microarray dataset. It is possible to use the Wilcoxon test statistic as the single filtering mechanism however calculation of the false positive rate is challenging (48). 

For each cluster, all combinations are calculated as described above. However, this is done for each experiment (time point) separately. Once all combinations are calculated, a Wilcoxon test is done to distinguish differences between the two different states (in our case control vs. drug). For each cluster, this is done for every calculated combination. Once all Wilcoxon tests for all clusters and all combinations are done, the P values are corrected for multiple testing. The clusters are then ranked according to the lowest P value that was achieved for the respective clusters. 

In case that both data sets to be compared are normally distributed the F-test is applied. The hypothesis of homogeneity of variance of both test series is eliminated when the significance level for homogeneity of variance is 5 %. The t-test for paired and non-paired data is performed when homogeneity of variance is present. In any case, a paired difference test (for paired data) or the U-test (for non-paired data) is likewise carried out (paired of difference test = Wilcoxon test U-test = Wilcoxon-Mann-Whitney or Mann-Whitney test, respectively). 

Test whether differences between feeding times at different concentrations are significant, using Friedman two-way analysis of variance. For comparison of particular pairs of treatments, use the Wilcoxon test. 

An example is found in an analysis of capecitabine and its metabolites in 505 subjects with solid tumors. Gieschke et al. (2003) placed 66% of all data into the model development set and the remainder into the validation data set. They then used the Wilcoxon test for... 

Rank test. A statistical test, such as the Mann-Whitney-Wilcoxon test, carried out on the ranks of the data rather than on the original data. Thus, the statistic used in the test, the rank statistic, is calculated from ranks of the data. Usually such tests are associated with randomization. Given knowledge of the randomization procedure, the distribution of the rank statistic is perfectly general under the null h5q)othesis. The rank is but the guinea stamp. The Mann s the gowd for a that (Burns). 

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