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Results for “Data Interpretation, Statistical”

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At least 1,207 records · Page 67Linked to original sources
PubMed2001

Interpretation, design, and analysis of gene array expression experiments.

Experiments using arrays of cDNA targets to compare patterns of gene expression are beginning to play a prominent role in biogerontology, but drawing reliable conclusions from the resulting data sets requires careful application of statistical methods that discriminate chance events from those likely to reflect real differences among the samples under study. This essay discusses flaws in the logic of studies that base their conclusions on ratio calculations alone, reviews the multiple comparison traps inherent in high throughput systems that test a very large number of mRNAs simultaneously, and advocates a two-stage design in which significance testing applied to exploratory data is used to guide a second round of hypothesis-testing experiments conducted in a separate set of experimental samples.

Aging↗
PubMed2006

Identification of functional, endogenous programmed -1 ribosomal frameshift signals in the genome of Saccharomyces cerevisiae.

In viruses, programmed -1 ribosomal frameshifting (-1 PRF) signals direct the translation of alternative proteins from a single mRNA. Given that many basic regulatory mechanisms were first discovered in viral systems, the current study endeavored to: (i) identify -1 PRF signals in genomic databases, (ii) apply the protocol to the yeast genome and (iii) test selected candidates at the bench. Computational analyses revealed the presence of 10 340 consensus -1 PRF signals in the yeast genome. Of the 6353 yeast ORFs, 1275 contain at least one strong and statistically significant -1 PRF signal. Eight out of nine selected sequences promoted efficient levels of PRF in vivo. These findings provide a robust platform for high throughput computational and laboratory studies and demonstrate that functional -1 PRF signals are widespread in the genome of Saccharomyces cerevisiae. The data generated by this study have been deposited into a publicly available database called the PRFdb. The presence of stable mRNA pseudoknot structures in these -1 PRF signals, and the observation that the predicted outcomes of nearly all of these genomic frameshift signals would direct ribosomes to premature termination codons, suggest two possible mRNA destabilization pathways through which -1 PRF signals could post-transcriptionally regulate mRNA abundance.

Base Sequence↗
PubMed1996

The use and interpretation of the Friedman test in the analysis of ordinal-scale data in repeated measures designs.

The purpose of this paper is to review the use and interpretation of the Friedman two-way analysis of variance by ranks test for ordinal-level data in repeated measurement designs. Physical therapists frequently make three or more repeated measurements of the same individual to compare different treatments, or to assess the effect of a single treatment over time. When the measurements are ordinal-scaled, such as some ratings of functional status and muscle strength, statistical significance may be determined by the Friedman test. We illustrate the use of the Friedman test and a post hoc multiple comparison test with data from 27 subjects whose performance on a lifting task was rated on three occasions by use of an ordinal scale. We discuss the interpretation of ordinal-level data and recommend that therapists understand the limitations a measurement scale imposes on the inferences that can be made from these tests.

Analysis of Variance↗
PubMedDate not supplied

A review of time-series studies used to evaluate the short-term effects of air pollution on human health.

We review the methodology used in the analysis of time-series studies of ambient air pollution. Our focus is on mortality studies, in which daily counts of death are correlated with changes in air pollution. We first illustrate the methods by showing data from the 1950s, during which the effects of air pollution were much more pronounced, and then describe current methods that were developed to identify associations when the signal-to-noise ratio is much lower. We describe basic data sources, details of statistical methods, and current state of the art, especially as it refers to problems found recently with the fitting algorithm used in the generalized additive models. A summary of the findings from mortality studies is presented and the pre-eminent issues regarding methods, interpretation, and identification of susceptible populations are discussed. We conclude by describing possible biological mechanisms and suggesting other designs that will aid in the interpretation of data from studies of acute health effects.

Air Pollutants↗
PubMed2004

Interpreting and reporting results.

Creating and disseminating knowledge is the goal of research. This is accomplished through critical analysis of systematically collected and clearly reported information. Critical analysis begins with the simple step of looking at the data collected prior to applying complex statistical analysis to make comparisons. Statistical analysis is approached in a standardised manner, depending on the type of data that has been collected. When a careful, stepwise standardised approach is applied to comparisons needed to address the research question, new knowledge is created and erroneous conclusions avoided. Following careful examination and analysis of the data, critical review is an important additional step to ensure that conclusions are correctly drawn. The process of peer review involved in publishing the research in the scientific literature is an important step to disseminating the new knowledge and ensuring its quality. Research is never complete without submitting it for publication in the peer-reviewed literature.

Data Interpretation, Statistical↗
PubMed2001

Mapping 137Cs deposition: data validation methods and data interpretation.

The "Atlas of caesium deposition on Europe after the Chernobyl accident" was prepared within the framework of the Joint Study Project 6 (JSP6) of the collaborative programme on the consequences of the Chernobyl accident between the European Commission and the Ministries responsible for Chernobyl affairs in Belarus, Russia and Ukraine. The radiological data provided by scientific institutes and competent authorities of more than 30 European countries were integrated into an information platform. Data validation and intercomparison were therefore essential before the interpretation of the deposition with the help of isoline maps prepared with a geographic information system (GIS) could be done. The data validation was a two-step procedure: after performing a primary logical consistency check, other techniques based on spatial statistics were used to outline uncertain data. The purpose of this paper is to present these validation methods and to discuss the advantages and constraints of these techniques. Rather than trying to improve the techniques of spatial data analysis, suggestions are made on how an adaptation of the sampling information could improve the final result.

Cesium Radioisotopes↗
PubMed2000

Bayesian statistics in medical research: an intuitive alternative to conventional data analysis.

Statistical analysis of both experimental and observational data is central to medical research. Unfortunately, the process of conventional statistical analysis is poorly understood by many medical scientists. This is due, in part, to the counter-intuitive nature of the basic tools of traditional (frequency-based) statistical inference. For example, the proper definition of a conventional 95% confidence interval is quite confusing. It is based upon the imaginary results of a series of hypothetical repetitions of the data generation process and subsequent analysis. Not surprisingly, this formal definition is often ignored and a 95% confidence interval is widely taken to represent a range of values that is associated with a 95% probability of containing the true value of the parameter being estimated. Working within the traditional framework of frequency-based statistics, this interpretation is fundamentally incorrect. It is perfectly valid, however, if one works within the framework of Bayesian statistics and assumes a 'prior distribution' that is uniform on the scale of the main outcome variable. This reflects a limited equivalence between conventional and Bayesian statistics that can be used to facilitate a simple Bayesian interpretation based on the results of a standard analysis. Such inferences provide direct and understandable answers to many important types of question in medical research. For example, they can be used to assist decision making based upon studies with unavoidably low statistical power, where non-significant results are all too often, and wrongly, interpreted as implying 'no effect'. They can also be used to overcome the confusion that can result when statistically significant effects are too small to be clinically relevant. This paper describes the theoretical basis of the Bayesian-based approach and illustrates its application with a practical example that investigates the prevalence of major cardiac defects in a cohort of children born using the assisted reproduction technique known as ICSI (intracytoplasmic sperm injection).

Bayes Theorem↗
PubMed2005

Basic concepts of statistical analysis for surgical research.

Appropriate statistical analyses are an integral part of surgical research. The purpose of this work is to assist surgeons and clinicians with the interpretation of statistics by providing a general understanding of the basic concepts that lead to choosing an appropriate statistical test for common study designs. It is extremely important to understand the nature of the data before embarking on a statistical analysis. A researcher must design an appropriate study around the research hypothesis. Initially, data should be inspected using frequency distributions and graphical techniques. If the data are continuous, the normality of the distribution must be assessed. In addition, the data must be defined as independent or dependent. For normally distributed and independent samples, a two-sample t test is appropriate. A paired t test should be used for dependent data. The nonparametric counterpart to the t test is the Mann-Whitney U and the paired counterpart is the Wilcoxon signed rank. For binary data, contingency table methods such as a chi2 test apply unless the expected value is < 5; then, use the Fisher's exact test. The McNemar test applies to paired binary data. Correlation coefficients assess the association between two continuous distributions. Linear regression assesses trend. Multiple regression analysis is appropriate for multivariate analyses with a continuous outcome variable. Logistic regression methods would apply for binary outcomes. The quality of the analysis and subsequent results of any research project depend on an appropriate study design, data collection, and analysis to make meaningful conclusions.

Biomedical Research↗
PubMed1990

Autosomal dominant retinitis pigmentosa: linkage to rhodopsin and evidence for genetic heterogeneity.

Retinitis pigmentosa (RP) is the most prevalent human retinopathy of genetic origin. Chromosomal locations for X-linked RP and autosomal dominant RP genes have recently been established. Multipoint analyses with ADRP and seven markers on the long arm of chromosome 3 demonstrate that the gene for rhodopsin, the pigment of the rod photoreceptors, cosegregates with the disease locus with a maximum lod score of approximately 19, implicating rhodopsin as a causative gene. Recent studies have indicated the presence of a point mutation at codon 23 in exon 1 of rhodopsin which results in the substitution of histidine for the highly conserved amino acid proline, suggesting that this mutation is a cause of rhodopsin-linked ADRP. This mutation is not present in the Irish pedigree in which ADRP has been mapped close to rhodopsin. Another mutation in the rhodopsin gene or in a gene closely linked to rhodopsin may be involved. Moreover, the gene in a second ADRP pedigree, with Type II late onset ADRP, does not segregate with chromosome 3q markers, indicating that nonallelic as well as perhaps allelic genetic heterogeneity exists in the autosomal dominant form of this disease.

Amino Acid Sequence↗