Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Statistics”

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 1,459 records · Page 81Linked to original sources
PubMed1993

Infant mortality statistics do not adequately reflect the impact of short gestation.

OBJECTIVE: To determine the accuracy of National Center for Health Statistics cause-specific infant mortality data. The National Center for Health Statistics compiles these data by applying World Health Organization (WHO) selection rules to death certificate data. The WHO rules arrange medical entities into a hierarchical order and select a single underlying cause of death (ULCD). DESIGN: A comparison was made between ULCD assigned to a cohort of 335 infant death certificates by (1) a neonatologist panel, and (2) application of WHO selection rules by the Florida State Office of Vital Statistics (OVS). RESULTS: Among the 146 infants with birth weights 1500 to 4649 g, agreement between neonatologists and OVS was 88%, while among the 189 infants with birth weights 0 to 1499 g (very low birth weight), agreement was just 41%. Neonatologists selected short gestation as the underlying cause of death for 82% of very low birth weight infant records, vs 25% by OVS. Due to the application of specific WHO selection rules, OVS frequently selected immediate causes of death, such as "cardiac arrest," as the ULCD, even when the medical certifier had indicated short gestation as the ULCD. In vital statistics reports, many of these immediate causes are reported as "other respiratory conditions of newborn," or "all other perinatal conditions." CONCLUSION: WHO ULCD selection rules should be modified to allow short gestation to have a higher priority over immediate causes of infant death.

Birth Weight↗
PubMed1977

The significance of cytotoxicity of lymphocyte populations in coloncarcinoma patients in comparison to normal controls using a new statistical method of evaluation.

Lymphocytotoxicity was studied in patients suffering from colon carcinoma. 125Iododeoxyuridin-labeled established colon carcinoma cells were used as target cells in a cytotoxicity assay according to COHEN et al. (1). They were incubated with unfractionated lymphocytes of the peripheral blood, purified T cells or adherent cells as effector cells. The cytotoxic effect was measured in cpm, i. e. the radioactivity released from the target cells into the supernatant. The cpm were adjusted by eliminating the variables of spontaneous release and for maximal incorporated radioactivity of the target cells. The cytotoxic activity of lymphocytes to colon carcinoma target cells was dose-dependent. It was demonstrated for lymphocytes from colon carcinoma patients as well as for lymphocytes from healthy controls. Although adjusted cpm values were used for statistical analysis lymphocytes from the 20 colon carcinoma patients did not show a higher cytotoxic effect than lymphocytes from the 20 healthy controls. However, when the results were compared separately for each experiment consisting of 2 colon carcinoma patients and 3 healthy controls, statistical significant specific lymphocytotoxicity was demonstrated for lymphocytes from colon carcinoma patients. The plot diagram of the results and the statistical evaluation by the multivariate analysis of variance (Manova) offer a clear and comprehensible representation of the results. Particularly for statistical reasons, this representation is superior to the usual calculation of percent specific lysis. It was demonstrated in this study that the cytotoxic activity in the absence of autologous serum is a function of T cells of the peripheral blood. Adherent cells have a high cytotoxic activity regardless whether the cells were obtained from colon carcinoma patients or from healthy controls.

Adenocarcinoma↗
PubMed1995

Study design, statistical analyses, and results reporting in the bone marrow transplantation literature.

To assess the statistical methods in the bone marrow transplantation (BMT) literature, we reviewed 255 articles from eight major journals (Annals of Internal Medicine, Blood, British Journal of Cancer, Cancer, Lancet, Journal of Clinical Oncology, New England Journal of Medicine, and Transplantation) between 1990 and 1992. Study designs, quality of statistical methods, and types of statistical procedures employed were summarized. There were similar percentages of case series (24%) and prospective trials (28%); however, the former design is often lacking in rigor of patient selection and treatment, and may therefore be less convincing. The reporting of eligibility criteria, treatment complications, and losses to follow-up was complete in the majority of articles (72-94%). Deficits in reporting were seen in power and sample size justifications (86%) and in stating whether the alternative hypothesis of the study was one-sided or two-sided (75%), information without which the magnitude of the p value cannot be interpreted. Although there has been recent emphasis on the evaluation of cost-effectiveness and quality of life as important endpoints, only 4-5% of the articles included these topics. Survival analysis was the most frequently employed technique (69%), and regression modeling (Cox and logistic) was also among the more common statistical techniques. The methods reported, however, often were inadequate to demonstrate that these techniques had been correctly applied and therefore that the results were correctly interpreted. Guidelines to further strengthen the design, analysis, and reporting of future BMT research are presented.

Bone Marrow Transplantation↗
PubMed1976

Epidemiology of hyaline membrane disease in the United States: analysis of national mortality statistics.

National mortality statistics for hyaline membrane disease (HMD) and respiratory distress syndrome (RDS) were examined in this study for the years 1968 to 1973. Detailed data were obtained by computer analysis of magnetic tapes from the National Center for Health Statistics. During the six-year interval, HMD/RDS was determined to be the underlying cause of death in 54,064 infants or 9,010 +/- 560 (mean +/- SD) infants per year. Analysis of individual death certificates for 1968 revealed the disease to a major contributing factor in another 24%. Thus, it may be estimated that HMD was involved in the demise of nearly 12,000 neonates per year over this period. This amounts to approximately 20% of all neonatal deaths. On the basis of mortality rates, a trend toward an increased incidence of fatal HMD/RDS was established from 1968 to 1973. Deaths tend to cluster in the summer months and January-February represent the lowest months of recorded fatalities. Analysis of the age at death, reflecting time course of the disease, revealed idential patterns for 1968 to 1970. The number of deaths was found to decline exponentially between the first and fourth 24-hour periods so that 92% of all deaths occurred by 4 days of age. Boys contributed more prominently to the death totals than girls with ratios from 1.62 to 1.76. Examination of mortality rates by race suggested that black permatures have a lower incidence of fatal HMD/RDS. In addition to nationwide figures, those of individual states were compared for three years. Generally, HMD/RDS mortality rates correlated with overall neonatal mortality statistics. Exceptions were observed, however, such as Illinois where low rates for the former coexist with relatively high neonatal death rates. These data respresent the first national mortality statistics for HMD and may prove useful in planning and providing intensive neonatal care.

Black People↗
PubMedDate not supplied

Coefficient of accuracy and concordance correlation coefficient: new statistics for methods comparison.

A new statistic, the Coefficient of Accuracy, C(a), has been developed by Lin for methods comparison. When an old measurement method is compared to a new measurement method or if the same method is compared in two laboratories, the Coefficient of Determination, r2, is typically used to measure the relationship. However, r2 only measures the precision of the relationship. The newly developed statistic, C(a), measures the accuracy of the relationship. When these two statistics are combined together, they form a single statistic for both accuracy and precision called the Concordance Correlation Coefficient, rc.

Algorithms↗
PubMed1998

Submicrovolt flicker electroretinogram: cycle-by-cycle recording of multiple harmonics with statistical estimation of measurement uncertainty.

PURPOSE: To study cycle-by-cycle recording of small-amplitude flicker-electroretinogram (ERG) responses and analyze results with robust statistical methods to estimate the measurement uncertainty. METHODS: Flicker ERGs at 32 Hz were recorded simultaneously from both eyes of patients with retinal degeneration. The ERG was amplified under wide-band (1-1000 Hz) conditions, digitized at 6144 Hz/eye, and multiplied point for point (192 points/cycle) by sine and cosine functions within each 1/32-second flash cycle to extract coefficients for six harmonic components of a discrete Fourier transform in real time. Amplitude windowing was not used, and all data were saved for subsequent statistical processing to identify and remove large-amplitude artifacts discretely and to search for quiet recording periods that minimized small-amplitude noise. RESULTS: Plots of amplitude and phase indicated far outlying noise points that were excised from the data. The SD of sequential intervals on a time line of the sine component identified quiet periods that minimized small-amplitude noise and improved measurement consistency. The SE of the response mean provided an estimate of measurement uncertainty. CONCLUSIONS: The harmonic components of many individual responses are captured quickly (e.g., 500 responses in 15.6 seconds) for post hoc statistical analysis, using mathematical algorithms that are precisely reproducible to facilitate comparison of results from all laboratories. Graphical time lines of responses allow separation of artifact transients from gaussian noise for elimination of noisy periods without disturbing the stored information. Statistical estimates of measurement uncertainty are determined on-line to allow immediate feedback during the recording session. Amplitude-phase plots of the multiple harmonic components, along with reconstructed analog waveforms, provide results in a readily assimilated manner for comparison of all testing sessions.

Electroretinography↗
PubMed1998

Statistical power analysis for PET studies in humans.

UNLABELLED: Although simple techniques have been established to determine statistical power when comparing, for example, the means of two groups of sampled data, the analysis is more complicated when establishing a trend in the data, such as with a linear regression. We present an approach to calculate the sample size necessary to reject the hypothesis that there is no trend in the data (slope is not different from zero) at a given level of statistical significance, given the intra- and inter-subject variability of the measurement. METHODS: We have derived analytically the distribution of the t statistic, for a given non-zero slope, and integrated this distribution to determine in what fraction of trials a real trend in the population would be missed. We illustrate our approach by re-examining the issue of an age-related impairment in presynaptic dopamine metabolism as measured by PET. RESULTS: We showed that the sample size necessary to determine whether 6-18F-fluoro-L-dopa retention decreases with age depends critically on both the variability of the quantitative method used and on the magnitude of the expected change. CONCLUSION: The method we have illustrated is a simple statistical test that allows investigators to be certain that an experimental design has a sufficient sample size to demonstrate the effect under study.

Age Factors↗
PubMed2002

How statistical expertise is used in medical research.

CONTEXT: Investigation of the nature and frequency of statistician involvement in medical research and its relation to the final editorial decision. METHODS: Authors of original research articles who submitted to BMJ and Annals of Internal Medicine from May through August 2001 were sent a short questionnaire at the time of manuscript submission. Authors were asked if they received assistance from a person with statistical expertise, the nature of any such contribution, and reasons why, if no statistical input was received. RESULTS: The response rate was 75% (704/943); methodological input was reported for 514 (73%) of these papers. In 435 papers (85%), such input was provided by biostatisticians or epidemiologists and, if deemed significant, was typically associated with authorship. A total of 33 of 122 methodologists (27%) whose main contribution started at the analysis stage received neither acknowledgment nor authorship. Research without methodological assistance was more likely to be rejected without review (71% vs 57%; chi(2) = 10.6; P =.001) and possibly less likely to be accepted for publication (7% vs 11%; chi(2) = 2.37; P =.12). CONCLUSIONS: Statistical input to medical research is widely recommended but inconsistently obtained. Individuals providing such expertise are often not involved until the analysis of data and many go unrecognized by either authorship or acknowledgment.

Authorship↗
PubMed1996

Statistical approaches to human brain mapping by functional magnetic resonance imaging.

Proper use of functional neuro-imaging through effective experimental design and modern statistical analysis provides new insights in current brain research. This tutorial has two aims: to describe aspects of this technology to applied statisticians and to provide some statistical ideas to neuroscientists unfamiliar with quantitative analytic methods that accommodate randomness. Introductory background material and ample references to current literature on the physics of magnetic resonance imaging, Fourier methods for image reconstruction and measures of image quality are included. Two of the statistical approaches mentioned here are extensions of established methods for longitudinal data analysis to the frequency domain. A recent case study provides real-world instances of approaches, problems and open questions encountered in current functional neuro-imaging research and an introduction to the analysis of spatial time series in this context.

Algorithms↗
PubMed1999

A simple allele sharing statistic for multiple locus systems.

For complex disorders where the actions of several interacting loci must be taken into account, current methods of joint linkage analysis are problematic. We have undertaken an exploration of simultaneous search statistics originally proposed by Dupuis et al. [1995]. Additionally, we have extended these methods slightly and propose here a simple simultaneous search statistic based upon the single-point allele sharing statistic calculated from GENEHUNTER (GH). The use of conditional search techniques is also explored.

Alleles↗
PubMed1999

Multipoint linkage analysis using the weighted-pairwise correlation statistic.

The weighted pairwise correlation (WPC) approach provides simple and flexible non-parametric tests for genetic linkage which may be adapted to qualitative, quantitative or age-dependent traits. Although this statistic has often been used with identity-by-state (IBS) information, there is much to gain by using multipoint identity-by-descent (IBD) information. The purpose of this paper is to use the unified multipoint approach of Kruglyak et al. [1996] with the WPC statistic. We used the simulated data of a complex disease proposed in GAW11 (problem 2) to validate this approach and to compare the multipoint WPC to the IBS-WPC and to the multilocus approach using the conventional non-parametric statistics S(pairs) and S(all). The results suggest that the multipoint WPC may be the most powerful approach.

Genetic Linkage↗
PubMed2005

Bridging the gap between statistical analysis and decision making in public health research.

Statisticians have eagerly taken on the role of presenting statistical summaries of quantitative data. In areas of health, this means providing point and interval estimates for quantities of interest such as diagnostic risks and treatment effects or providing curve estimates for quantities of interest such as survival probabilities across time. Methods for providing such summaries are highly formalized and constantly evolving. While decision making is the incentive for nearly all such efforts, the process that transforms statistical summaries into decisions usually remains informal and ad hoc. Statisticians have not eagerly accepted the role of promoting formalized decision-theoretic techniques. This paper will argue that the gap between statistical synthesis and decision making is an unnatural and undesirable one, because it undermines the impact of quantitative information. An argument for bridging the gap by expanding the role of statisticians will be presented.

Bayes Theorem↗
PubMed1994

Stratification of summary statistic tests according to missing data patterns.

Summary statistics, such as slope or area under the time-response curve, reduce the dimensionality of repeated measures data and can thereby simplify the comparison of groups in longitudinal studies. Since summary statistic distributions vary according to the amount, timing, and type of any missingness that occurs, one must choose between analysing the data unconditionally or conditionally on the missingness patterns. This paper uses simulations to compare such unstratified and stratified summary statistic analyses with respect to their size and power under models that allow for both non-informative and informative missingness mechanisms. Of particular interest is the robustness of these methods to violations of the assumptions that one must make if they are to have proper test size. It is found that stratification of the analysis tends to result in an increase of power, and improves the robustness to violations of missing data assumptions.

Computer Simulation↗
PubMed1991

Statistical methods for analyzing developmental toxicity data.

A description and review of methods for performing per-litter analyses involving extrabinomial proportion response is provided. It is stressed that the litter should be regarded as the appropriate experimental unit for quantitative analysis in studies for teratogenic or heritable mutagenic effects. Attention is directed at statistical identification of possible treatment effects, such as a positive dose response to a chemical stimulus. The methods range from distribution-free, nonparametric analyses to models involving parametric distributions such as the beta-binomial density. It is seen that most current methods require computer implementation. When concern is raised over misspecification of assumptions critical to the statistical analysis, it is argued that relatively parameter-free methods are appropriate for use. These include statistical bootstrapping and rank-based analyses.

Models, Statistical↗
PubMed1993

A statistical test of compatibility of data sets to a common dose-response model.

Quantitative estimates of cancer risk generally involve low-dose extrapolation based on an exponential dose-response model for dichotomous response data. Frequently more than one data set is available. If a careful analysis of the biological issues indicates that more than one of the available data sets could be used in the quantitative estimate of cancer risk, it is reasonable to think of combining the data. Before combining data, however, it would be prudent to test whether the data sets are compatible with a common dose-response model. If they are not, it could be concluded that an underlying biological factor is responsible. If they are statistically compatible, the decision to combine data sets based on biological issues would be reinforced. A statistical test based on the generalized likelihood ratio method is proposed for evaluating the compatibility of different data sets with a common dose-response model. This method of constructing a statistical test and the associated asymptotic theory is consistent with the approach used by GLOBAL86 (R. B. Howe, K. S. Crump, and C. Van Landingham, GLOBAL86: A Computer Program to Extrapolate Quantal Animal Toxicity Data to Low Doses, K. S. Crump & Co., Ruston, LA, 1986) for estimating the confidence limits that are used as a basis for quantitative estimates.

Animals↗
PubMed2003

Words in DNA sequences: some case studies based on their frequency statistics.

One of the critical requirements of data analysis involving large DNA sequences is an effective statistical summarization of those sequences. In this article DNA sequences have been analyzed based on word frequencies. Our analysis focuses on the detection of structural signature of a genome reflected in word frequencies and identification of phylogenetic relationships among different species reflected in the variation of word distributions in their DNA sequences. We have carried out a statistical study of the complete genome of baker's yeast, of various ribosomal RNA sequences from different prokaryotic and eukaryotic organisms and of the full genomes of some bacteriophages. Our exploratory analysis amply demonstrates the usefulness of DNA word frequencies in reducing the dimensionality of large sequences while retaining some of the structural information there that can have biological significance. Some conceptual issues that arise in course of our investigation have been addressed. A few interesting problems related to the statistics of DNA words have been pointed out with some indication of their possible solutions. The work has been partially motivated by the fact that sequence alignment and homology techniques that are quite popular for comparing and analyzing relatively smaller DNA sequences of nearly equal sizes are not applicable to data consisting of large sequences with widely varying sizes, which may contain segments with unknown or no biological functions, and consequently their comparison through functional homology is either impossible or extremely difficult.

Bacteriophages↗
PubMed1977

A new procedure for the statistical evaluation of intrauterine contraception.

An improved statistical method for assessing the efficacy of intrauterine contraception is presented. This method, called the log-rank method, is based on a daily life table, which yields the best estimates of the cumulative net termination probabilities. It provides a sensitive chi-square test statistic to detect differences among these probabilities for two or more contraceptive devices. When three or more devices are compared, the chi-square statistic may be partitioned into additive components representing comparisons among groups of devices. The log-rank method also permits adjusting for differences among subgroups by controlling for factors such as parity or age. Although calculations may be performed on a desk calculator, a FORTRAN-IV computer program is made available to interested researchers.

Computers↗
PubMed1989

Statistical evaluation of agreement between two methods for measuring a quantitative variable.

Methodologic research is often concerned with determining whether two methods (procedures, laboratory instruments) can be used interchangeably for measuring some quantitative variable of interest. Logically, one method can be used as a surrogate of another provided the methods show high agreement on the measured results. Although the product-moment correlation (r) is often used as an indicator of agreement, this index is in fact inappropriate for this purpose. The intraclass correlation (r1) is the correct statistic for assessing agreement or consistency between two methods. Another criterion sometimes used for supporting interchangeability is the similarity of the mean measured results obtained by the two methods. However, similarity of means (aggregate agreement) does not necessarily indicate individual-subject agreement, and it is the latter that is the pre-requisite for interchangeability. On the other hand, a marked difference between two means (lack of aggregate agreement) does necessarily indicate lack of individual-subject agreement and therefore non-interchangeability. Herein we suggest that two methods for measuring a quantitative variable can be judged interchangeable provided all of the following conditions are met: first the methods must not exhibit marked additive or nonadditive systematic bias; second the difference between the two mean readings is not "statistically significant"; third, the lower limit of the 95% confidence interval of the intraclass correlation is at least 0.75. Statistical procedures to evaluate these conditions of interchangeability are described in detail. A computer program coded in SAS to carry out the procedures is listed in the Appendix. A similar program coded in DBASE III PLUS for the microcomputer is available upon request.

Analysis of Variance↗