Bmc Med Res Methodol
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Bmc Med Res Methodol · Jan 2005
Comparative StudyAdaptive designs based on the truncated product method.
Adaptive designs are becoming increasingly important in clinical research. One approach subdivides the study into several (two or more) stages and combines the p-values of the different stages using Fisher's combination test. ⋯ It is recommended to apply the TPM rather than Fisher's combination test whenever an early termination due to insufficient effects is not suitable within the adaptive design.
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Bmc Med Res Methodol · Jan 2005
Comparative StudyLack of interchangeability between visual analogue and verbal rating pain scales: a cross sectional description of pain etiology groups.
Rating scales like the visual analogue scale, VAS, and the verbal rating scale, VRS, are often used for pain assessments both in clinical work and in research, despite the lack of a gold standard. Interchangeability of recorded pain intensity captured in the two scales has been discussed earlier, but not in conjunction with taking the influence of pain etiology into consideration. ⋯ The pain intensity assessments on VAS and VRS are in this study, not interchangeable due to overlap of pain records between the two scales, systematic disagreements when comparing the two scales and a low percentage intra-scale agreement. Furthermore, the lower VAS cut-off positions relative the VRS labels indicate different meaning of the rated pain intensity depending on pain etiology. It is also indicated that the scales have non-linear properties and that the two scales probably have different interpretation. Our findings are in favor of using the VRS in pain intensity assessments but if still the VAS is preferred, the VAS data should be analyzed as continuous using statistical methods suitable for ordinal data. Furthermore, our findings indicate a risk to over or under estimate the patient's perceived pain when interpreting condensed VAS data.
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Bmc Med Res Methodol · Jan 2005
Parametric versus non-parametric statistics in the analysis of randomized trials with non-normally distributed data.
It has generally been argued that parametric statistics should not be applied to data with non-normal distributions. Empirical research has demonstrated that Mann-Whitney generally has greater power than the t-test unless data are sampled from the normal. In the case of randomized trials, we are typically interested in how an endpoint, such as blood pressure or pain, changes following treatment. Such trials should be analyzed using ANCOVA, rather than t-test. The objectives of this study were: a) to compare the relative power of Mann-Whitney and ANCOVA; b) to determine whether ANCOVA provides an unbiased estimate for the difference between groups; c) to investigate the distribution of change scores between repeat assessments of a non-normally distributed variable. ⋯ ANCOVA is the preferred method of analyzing randomized trials with baseline and post-treatment measures. In certain extreme cases, ANCOVA is less powerful than Mann-Whitney. Notably, in these cases, the estimate of treatment effect provided by ANCOVA is of questionable interpretability.
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Bmc Med Res Methodol · Jun 2004
The Platino project: methodology of a multicenter prevalence survey of chronic obstructive pulmonary disease in major Latin American cities.
The prevalence of Chronic Obstructive Pulmonary Disease (COPD) in many developed countries appears to be increasing. There is some evidence from Latin America that COPD is a growing cause of death, but information on prevalence is scant. It is possible that, due to the high frequency of smoking in these countries, this disease may represent a major public health problem that has not yet been recognized as such. The PLATINO study is aimed at measuring COPD prevalence in major cities in Latin America. ⋯ The PLATINO project will provide a detailed picture of the global distribution of COPD in Latin America. This project shows that studies from Latin America can be carried out with adequate quality and be of scientific value.
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Bmc Med Res Methodol · May 2004
Comparative StudyThe level of non-citation of articles within a journal as a measure of quality: a comparison to the impact factor.
Current methods of measuring the quality of journals assume that citations of articles within journals are normally distributed. Furthermore using journal impact factors to measure the quality of individual articles is flawed if citations are not uniformly spread between articles. The aim of this study was to assess the distribution of citations to articles and use the level of non-citation of articles within a journal as a measure of quality. This ranking method is compared with the impact factor, as calculated by ISI(R). ⋯ Ranking journals by impact factor and non-citation produces similar results. Using a non-citation rate is advantageous as it creates a clear distinction between how citation analysis is used to determine the quality of a journal (low level of non-citation) and an individual article (citation counting). Non-citation levels should therefore be made available for all journals.