Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Data Analysis”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,045 records · Page 58Linked to original sources
PubMed1988

Research methods in nutrition and dietetics: design, data analysis, and presentation.

Most problems in practice may be addressed through research. To show the applicability of research to all areas of nutrition and dietetics, seven types of research designs are discussed in this article: qualitative research; case series and surveys--both categorized as descriptive research; and experimental design, quasiexperimental design, cohort (follow-up) studies, and case-control studies--the four of which are categorized as analytical research because each design tests hypotheses of causal relationships. Sample size, subject selection, and statistical analysis and interpretation are discussed as appropriate to each research design. Numerous examples are presented, along with the basic research designs. Each section and subsection is numbered so that the article can serve easily as a reference and its component parts can be accessed readily. Research provides answers to questions and, generally, raises further questions that future research can address. Among the benefits of well-designed research are answers to clearly stated research questions, useful comparisons between options, information to guide evaluations of protocols, and data to document and support one's professional activities and one's staff.

Clinical Trials as Topic↗
PubMedDate not supplied

Data analysis for repeated measures studies.

Many research questions in nursing can best be answered by designing studies using repeated measures representing pretreatment and posttreatment observations on the same subject. In this article, the author discusses both a parametric statistical test and its nonparametric counterpart and provides guidance regarding when it is appropriate to use each. The steps used in computing both statistics are also provided.

Chi-Square Distribution↗
PubMedDate not supplied

Some practical issues in binary data analysis.

Three topics motivated by practical problems where the response variable is binary are described and illustrated. When a number of different explanatory variables are measured on each individual, a parsimonious model may be needed to predict the response of a future patient, or in selecting the variables that any treatment effect must be adjusted for. Some variable selection procedures used in conjunction with fitting logistic regression models are summarized and their performance investigated using a simulation study. A study to compare two devices for delivering anaesthetic gas to patients during surgery is then described, in which the response variable is the incidence of post-operative sore throat. In this study, the allocation of patient to device was non-random and a method for analysing these data that takes account of this aspect of the data is illustrated. In studies to compare different forms of contraceptive, the extent of regularity in the menstrual bleeding cycle is an important consideration for the acceptability of a contraceptive. Diary data on the menstrual bleeding pattern are therefore routinely collected. A method of summarizing the cyclic behaviour in the diary data for a particular woman is described, and extended to allow comparisons to be made between groups of women on different types of contraceptive. The approach is illustrated using a database made available by the World Health Organization.

Computer Simulation↗
PubMed2003

Sensitivity studies for quantitative assays: use of censored data analysis.

Probit regression analysis is frequently used to study the relation between the concentration of an analyte in a sample and the probability that the assay used yields a positive test result. For these analyses only the qualitative classification 'positive' or 'negative' is used, whereas, particularly in the case where the assay is quantitative in nature, the results contain more information. In the current paper, we propose an alternative method, in which the negative test results are treated as being (left) censored. As such, more efficient use is made of the information in the data. The procedures are illustrated using two generations of NucliSens assays (BioMérieux), which are designed to quantify the viral load of HIV-1 in blood samples. Computer simulations are used to illustrate some properties of the estimated parameters.

Blood Banks↗
PubMed2004

Strategies and data analysis techniques for lipid and phospholipid chemistry elucidation by intact cell MALDI-FTMS.

Ions attributed to lipids and phospholipids are directly observed by desorption from whole bacteria using intact cell (IC) matrix-assisted laser desorption-ionization (MALDI) Fourier transform mass spectrometry (FTMS). Saccharomyces cerevisiae are grown in rich media broth, concentrated, and applied directly to the MALDI surface without lysis or chemical treatment. FTMS of MALDI ions gives excellent signal to noise ratios with typical resolving powers of 90,000 and mass precision better than 0.002 Da. Use of accurate mass measurements and a simple set of rules allow assignment of major peaks into one of twelve expected lipid classes. Subsequently, fractional mass versus whole number mass plots are employed to enhance visual interpretation of the high-resolution data and to facilitate detection of related ions such as those representing homologous series or different degrees of unsaturation. This approach, coupled with rules based on bacterial biochemistry, is used to classify ions with m/z up to about 1000. Major spectral peaks in the range m/z 200-1000 are assigned as lipids and phospholipids. In this study, it is assumed that biologically-derived ions with m/z values lower than 1000 are lipids. This is not unreasonable in view of the facts that molecular weights of lipids are almost always less than 1000 Da, that the copy numbers for lipids in a cell are higher than those for any single protein or other component, and that lipids are generally collections of distinct homologous partners, unlike proteins or other cell components. This paper presents a new rapid lipid-profiling method based on IC MALDI-FTMS.

Membrane Lipids↗
PubMed2004

The effect of solvent on permeant diffusion through membranes studied using ATR-FTIR and chemometric data analysis.

One method of improving the bioavailability of a topical formulation is to add an appropriate solvent that will act as a solubilizer for the permeant and, at the same time, modify the barrier properties of the stratum corneum. It has proved very difficult to determine the precise mechanisms of action involved; this is complicated by the concurrent diffusion of the solvent and the permeant into the skin. Under these circumstances the barrier function may well be changing as a function of time as the solvent disrupts it. We have observed this phenomenon in a model silicone membrane system that we have chosen to study initially to avoid the complexity of the heterogeneous nature of skin and its inherent biological variability. Diffusion experiments were conducted using an established ATR-FTIR approach but the data interpreted using sophisticated chemometric approaches that allowed us to deconvolve the IR signals from the permeant, the solvent, and the membrane. Data are presented that show the concurrent diffusion of benzoic acid (permeant), octanol (solvent), and how the octanol modifies the characteristics of the silicone membrane. Initial data are then presented using human skin to show the power of the diffusion approach coupled to the data deconvolution technique.

Diffusion↗
PubMed1987

External quality assessment data analysis by microcomputer.

Microcomputers are now widely used in clinical laboratories because of their low price and the availability of a wide variety of software that can be adapted to the users' requirements. The continuously increasing numbers of patients, tests and the use of automation are additional factors which emphasize the need for computers. A microcomputer software that meets the exact requirements of the Quality Control Unit was developed to evaluate laboratories participating in the Kuwait National Bacteriological Quality Assessment Scheme.

Computers↗
PubMed1987

Kinetic data analysis with a noisy input function.

Methods of parameter estimation are proposed for the analysis of dynamic experiments in which the input function is noisy. Noise in the input function leads to uncertainties in the calculated model-predicted values, and therefore the covariance matrix of the residuals is a function of the model parameters. These statistical uncertainties in the model-predicted values significantly change the nature of the fitting process and the quality of the results. The proposed optimisation methods use weighted least-squares criteria, and three choices for the weighting matrix are considered. The proposed weighting matrices, in order of complexity are: (1) the identity matrix (no weighting), (2) the covariance matrix of the data (ignoring the noise in the input function), and (3) the full covariance matrix of the residuals (incorporating both the noise in the data and the noise in the input function). The methodology is applied to dynamic emission tomography studies of the heart, where the blood (input) and tissue tracer concentrations at each time are derived from two regions of interest in the same tomographic slice. Computer stimulations of compartmental systems show that parameters and their covariance matrix are more accurately estimated when the full covariance matrix of the residuals is used as a weighting matrix rather than either of the other two methods. For the practical example considered, parameter bias was increased by a factor of at least four when the noise in the input function was ignored, and one parameter had a bias of 24% when the unweighted least-squares criterion was used.

Computer Simulation↗
PubMed1999

A Bayesian hierarchical model for multi-level repeated ordinal data: analysis of oral practice examinations in a large anaesthesiology training programme.

Oral practice examinations (OPEs) are used in many anaesthesiology programmes to familiarize anaesthesiology residents with the format of the oral examination administered by the American Board of Anesthesiology. The OPE outcome (final grade) consists of 'Definite Not Pass', 'Probable Not Pass', 'Probable Pass' and 'Definite Pass'. In our study to assess the validity of the OPE, residents took an average of two (ranging from one to six) OPEs, each of which was evaluated by two board certified anaesthesiologists randomly selected from a pool of 12. A key question of interest was to identify factors, for example, the length of training, didactic experience and other characteristics, that most influence OPE outcome. In addition, we were interested in assessing the reliability of the final grade, that is, the covariance parameters are of interest as well. However, estimating variance components in multi-level data with an unequal number of repeated ordinal outcomes presents several statistical challenges, such as how to estimate high dimensional random effects parameters, especially for ordinal outcomes. We propose a Bayesian hierarchical proportional odds model for data with such complexity. The flexibility of such a model allows us to make inference on the association of OPE outcomes with other factors and to estimate the variance components as well.

Anesthesiology↗
PubMed2003

Correlation of the local and the macroscopic properties of high-temperature superconductors: EXAFS data analysis.

Based on temperature-dependent EXAFS studies of Ba(1-x)K(x)BiO(3) superconducting oxide, a model of the relationship between the local crystal and the local electronic structures has been proposed. Oxygen ions were found to vibrate in a double-well potential and their vibrations are correlated with the local electron pair transfer due to the dynamical exchange BiO(6) <--> BiL(2)O(6), where L(2) denotes the hole pair in the antibonding Bi 6s O2p(sigma*) orbital of the octahedral complex. The similarity of the EXAFS spectra features of Ba(1-x)K(x)BiO(3) and La(2-x)Sr(x)CuO(4) allowed us to propose a similar model for Cu-based superconducting oxides. The model, in a common approach, explains the antiferromagnetic state, metal-insulator phase transition and the appearance of superconductivity at Sr(2+) doping of La(2)CuO(4), and eliminates discrepancy between the neutron-scattering and EXAFS data.

Journal Article↗
PubMed1997

Dioxinlike components in incinerator fly ash: a comparison between chemical analysis data and results from a cell culture bioassay.

Potent polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxinlike polychlorinated biphenyls (PCBs) are among the most relevant toxic emissions from incinerators. Induction of cytochrome P450 1A1-catalyzed 7-ethoxyresorufin O-deethylase (EROD) activity in mammalian cell culture (EROD bioassay) is thought to be a selective and sensitive parameter used for the quantification of dioxinlike compounds. Fly ash extracts from municipal waste incinerators (MWI), a crematorium, wood combustors, and a noble metal recycling facility were analyzed in the EROD bioassay using rat hepatocytes in primary culture. Fractions containing 2,3,7,8-substituted PCDDs/PCDFs, dioxinlike PCBs, and 16 major polycyclic aromatic hydrocarbons (PAHs) were isolated from the extract and analyzed by gas chromatography-mass spectrometry (GC-MS) and by the EROD bioassay. It was found that with MWI samples the bioassay of the extract resulted in a two- to fivefold higher estimate of TCDD equivalents (TEQ) than the chemical analysis of PCDDs/PCDFs and PCBs. However, the outcome of both methods was significantly correlated, making the bioassay useful as a rough estimate for the sum of potent PCDDs/PCDFs and dioxinlike PCBs in extracts from MWI fly ash samples and in a fly ash sample from a crematorium. In noble metal recycling facility and wood combustor samples, higher amounts of PAHs were found, contributing to more pronounced differences between the results of both methods. The remaining unexplained inducing potency in fly ash samples probably results from additional dioxinlike components including certain PAHs not analyzed in this study. The hypothesis that emissions from MWI of hitherto unidentified dioxinlike compounds are higher by orders of magnitude than emissions of potent PCDDs/PCDFs and dioxinlike PCBs could not be confirmed. We found no indication for a marked synergistic interaction of dioxinlike fly ash components in the bioassay.

Air Pollutants↗
PubMed1991

Data analysis techniques in behavioral pediatrics: some practical advice.

A review of the last three volumes of the Journal of Developmental and Behavioral Pediatrics revealed that 27% of the articles used correlations, 17% chi 2, 16% t tests, 15% analysis of variance or covariance, and 13% involved regression analysis. Multivariate techniques, discriminant or factor analysis, logistic regression, and sensitivity/specificity were used in less than 5% of articles; the average number of statistical techniques per article was 2.5. These statistical techniques are described in general, conceptual terms in regard to appropriate and inappropriate usage. Clinical examples are provided. Familiarity with these techniques allows the reader "statistical access" to almost 90% of the articles in behavioral pediatrics and other areas of the medical literature.

Child↗
PubMed2004

7Li MR measures of blood lithium--correlation with chemical analysis data.

Lithium is used in the treatment and prophylaxis of manic-depressive illness. A narrow therapeutic range of lithium (0.4-1.2 meq/l) requires constant monitoring of these levels to avoid neurotoxicity and overdose. It is general practice to measure plasma lithium levels as a guide to monitor the therapy. Efforts to predict the concentration of Li at its active sites in the brain have led to the use of red blood cells (RBCs) because they are similar to neuronal cells. Thus RBC lithium is a very relevant clinical parameter for monitoring therapy and to observe the changes at intracellular levels under varying treatment conditions. A measure of both plasma and RBC lithium may be of significant value to physicians and researchers as lithium profile for RBCs correlate more closely with the brain lithium than plasma lithium. Although methods to measure lithium in blood such as atomic absorption or flame photometry exist, a complete quantitation of both plasma and RBC lithium requires a tedious physical separation of the two components prior to chemical analysis. On the other hand, lithium MR technique, via the use of shift reagents, can provide both plasma and RBC lithium in a single study. Here we have performed a correlation study of lithium results obtained from MR with the vitros dry-slide method on blood samples from rats treated with lithium. The results show a high degree of correlation between the two methods. Additionally, the MR measurements made on dilute samples of blood indicate that small blood samples with lithium concentration in the neighborhood of 0.08 meq/l can be measured with high accuracy and reproducibility needed for clinical purposes.

Animals↗
PubMed1990

Factors affecting prognosis of intrauterine hydrocephalus diagnosed in the third trimester--computerized data analysis on controversies in fetal surgery.

Twenty hydrocephalic patients diagnosed in the third trimester of fetal life were evaluated and followed during a 7-year period. The factors affecting the prognosis, including the type of hydrocephalus, underlying conditions, associated anomalies, time of diagnosis and delivery, fetal period after diagnosis, head circumference and degree of ventriculomegaly at birth, and age at treatment, were comprehensively analyzed. The difference between final outcomes as assessed by developmental quotient (DQ) or intelligence quotient (IQ) were statistically tested with computation by means of STAX packages in an NEC 9801 VX. Hydrocephalus as an isolated defect occurred in six cases (30%), was associated with other central nervous system anomalies in nine (45%), and was secondary to intrauterine intraventricular hemorrhage or brain tumor in five (25%). The average age at the time of diagnosis was 33.9 weeks of gestation (range, 27-40 weeks). One fetus was treated by transabdominal cephalocentesis, but the majority of patients underwent ventriculoperitoneal shunt postnatally. The final IQ or DQ scores ranged from 20 to 120 (mean score, 50.6). The data analyses revealed that the only significant factor affecting outcome was the fetal period after diagnosis of hydrocephalus (r = -0.5076, p less than 0.01). Our data supports the fact that the results of an on-going hydrocephalic state may become irreversible during fetal life. It is emphasized that establishment of a more precise pathophysiological evaluation, and a less invasive but more reliable decompressive technique for fetal hydrocephalus, is urgent.

Chi-Square Distribution↗
PubMed1992

Genetic transmission of colorectal cancer: exploratory data analysis from a population based registry.

Classical segregation analysis was conducted on 605 families of probands with colorectal carcinoma ascertained through the Cancer Registry of the Province of Modena in Italy. The families were classified as 28 suspected hereditary non-polyposis colorectal cancer (HNPCC) syndromes and 577 presumed non-HNPCC. In 11 of these, both parents had colorectal carcinoma, in 130 one parent was affected, and in 436 both parents were normal. In the suspected HNPCC families, segregation was compatible with dominant transmission of susceptibility to carcinoma. In families with one parent affected, the segregation frequency was almost exactly equal to the frequency of segregation in families where both parents were normal. The model of dominant transmission of susceptibility through a major gene with greatly reduced penetrance in heterozygotes fitted the data acceptably.

Colorectal Neoplasms↗
PubMed1983

Oral presentations in non-Hodgkin's lymphoma: a review of thirty-one cases. Part I. Data analysis.

Thirty-one patients with oral manifestations of non-Hodgkin's lymphoma have been studied with reference to age, sex, race, location of lesion in oral cavity, stage of disease on presentation, duration of disease at time of presentation, histologic type, modes of treatment, and survival. There were 6 children and 25 adults, ranging in age from 3 to 89 years. Only 2 of the 31 patients were black. Sex incidence was almost equal, with 17 females and 14 males. In 12 cases the oral findings alone represented the initial presentation of lymphoma. The maxilla, mandible, and palate accounted for 24 of the 31 cases. The preponderance of diffuse histologic patterns was striking (77.4 percent). Eighteen cases (58.0 percent) presented in Stage I or Stage II, indicating relatively limited extent of disease. More generalized involvement was found in the remaining thirteen cases (41.9 percent). Thus, although NHL may appear in the oral region as the first detected evidence of disease, in many patients a work-up will show that the process is widespread in distribution. In this brief series survival data coincide with the established principles that a poorer prognosis is associated with the diffuse histologic pattern, as well as certain identified histiocytic and poorly differentiated lymphocytic subtypes.

Adolescent↗
PubMedDate not supplied

Active-controlled, non-inferiority trials in oncology: arbitrary limits, infeasible sample sizes and uninformative data analysis. is there another way?

In oncology, it may not always be possible to evaluate the efficacy of new medicines in placebo-controlled trials. Furthermore, while some newer, biologically targeted anti-cancer treatments may be expected to deliver therapeutic benefit in terms of better tolerability or improved symptom control, they may not always be expected to provide increased efficacy relative to existing therapies. This naturally leads to the use of active-control, non-inferiority trials to evaluate such treatments. In recent evaluations of anti-cancer treatments, the non-inferiority margin has often been defined in terms of demonstrating that at least 50% of the active control effect has been retained by the new drug using methods such as those described by Rothmann et al., Statistics in Medicine 2003; 22:239-264 and Wang and Hung Controlled Clinical Trials 2003; 24:147-155. However, this approach can lead to prohibitively large clinical trials and results in a tendency to dichotomize trial outcome as either 'success' or 'failure' and thus oversimplifies interpretation. With relatively modest modification, these methods can be used to define a stepwise approach to design and analysis. In the first design step, the trial is sized to show indirectly that the new drug would have beaten placebo; in the second analysis step, the probability that the new drug is superior to placebo is assessed and, if sufficiently high in the third and final step, the relative efficacy of the new drug to control is assessed on a continuum of effect retention via an 'effect retention likelihood plot'. This stepwise approach is likely to provide a more complete assessment of relative efficacy so that the value of new treatments can be better judged.

Clinical Trials as Topic↗
PubMed2005

Using qualitative interviews in CAM research: a guide to study design, data collection and data analysis.

Qualitative methods, such as the in-depth interview, offer a potentially powerful means of uncovering the complex experiences of patients, carers and clinicians within treatment and decision-making processes. In the context of complementary and alternative medicine (CAM), qualitative interview-based projects allow for subjectivity and complexity within human experience, making them a powerful tool for increasing our knowledge of important processes within CAM. However, qualitative interview-based projects are often poorly designed, carried out and analysed. This article provides a guide for CAM researchers on how to use qualitative interviews to produce meaningful, and methodologically sound, research findings.

Complementary Therapies↗