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PubMed2005

[Linking quantitation of electrophoresis pattern and data analysis in AFLP for Oncomelania hupensis].

OBJECTIVE: To search into a method for analyzing the quantitative data in amplified fragment length polymorphism (AFLP) electrophoresis. METHODS: Oncomelania snails collected from the field were screened. Forty snails found uninfected with schistosomiasis were divided randomly into two groups and used to isolate genomic DNA. AFLP electrophoresis pattern was first transformed into quantitative data by Glyko BandScan software, and the bands were read according to different standards of band-reading to acquire the corresponding data. These data sets were analyzed by genetic statistics to get an inference set, and the analysis of this inference set was performed to reach a summary description. RESULTS: The results of genetic variation from different standards of band-reading were different With the increase of the standard value of band-reading, the indices indicating the genetic polymorphism of Oncomelania hupensis population (e.g. Shannon's information index) also increased. When the standard value reached at certain level, the values of these indices began to decrease. Compared with the above indices, the change for gene flow turned out contrary to the genetic identity. The distributions of inference results from different standards of band-reading all showed significant normal distribution. The mean value of genetic variation based on total grey was very close to that on the proportion of total grey. The average genetic identity between the "subpopulations" was 0.956 according to proportion of total grey or 0.958 from the total grey with an average genetic distance between the "subpopulations" of 0.045 and 0.043 respectively. CONCLUSION: It seems to be a reasonable and accurate method by quantifying the AFLP electrophoresis pattern followed by analyzing the data through the use of the different standards of band-reading.

Animals↗
PubMed2000

Exploring a critical parameter of timing in the mouse cerebellar microcircuitry: the parallel fiber diameter.

Since the conduction velocity of the parallel fibers is a critical parameter for a theory of timing in the cerebellar cortex, we set out to quantify the diameter of these axons on an ultrastructural level. The overall mean of the fiber diameter was 0.18 microm. Our results confirm that the parallel fibers of the upper molecular layer are significantly thinner than those of the lower layers. Nevertheless, the difference of about 0.02 microm determined by this study is surprisingly small. In addition, the distribution of the fiber diameters of the upper layers differed slightly, but significantly from a normal distribution, partly on account of a positive skew and a positive kurtosis excess. In summary, the results show that there are fewer differences between the parallel fibers of different levels of the molecular layer than previously assumed and that these differences do not contradict a theory of timing in the cerebellar cortex.

Animals↗
PubMed1990

EEG amplitudes in healthy, late-middle-aged and elderly adults: normality of the distributions and correlations with age.

The interindividual distributions of EEG amplitudes were evaluated in 60 healthy subjects, aged 56-76. Skew and kurtosis were used to assess the normality of the amplitude distributions in 5 frequency bands (delta, theta, alpha and 2 beta ranges) and 28 scalp derivations while the subjects were awake and rested with their eyes closed and opened. Most of the interindividual EEG amplitude distributions were not normally distributed. Two transformations were applied to the EEG amplitudes: the square root and the natural logarithm. Evaluation of skew and kurtosis indicated that the natural logarithmic transformation was more effective than the square root in reducing the positive skew and leptokurtosis that characterized the untransformed interindividual EEG amplitude distributions. For all frequency bands except theta, the log transformation rendered the distributions approximately normal in form. Correlations between log transformed EEG amplitudes and age were not statistically significant. These findings are discussed in the context of previous research, aging, and methodological features.

Aged↗
PubMed1996

The shape of the distribution of the number of sexual partners.

Information on the number of sexual partners that people have is necessary for predicting the likely long term course of the AIDS epidemic. More information is required than is provided by simply stating the mean and variance of the number of partners. It is useful to find a family of curves which approximate data on the proportion of people in the various 'number of partners' categories. Two Australian surveys of the sexual behaviour of first year university behavioural science students were analysed. It was found here that log-normal distributions gave good approximations to the distribution of number of partners amongst people who had more than one partner. Gamma and negative binomial distributions gave less satisfactory fits and the truncated normal and Poisson distributions were clearly unable to match the data.

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

[Neonatal weight: an analysis of the distribution].

We examined birthweight distribution in relation to gestational age from 25 to 42 weeks in a series of 3.526 single newborns and in whom reliability of gestational age was rigorously controlled. To verify the distribution normality the Shapiro-Wilk and the Kolmogorov tests have been applied. Birthweight data follow a gaussian distribution for each gestational age week. Therefore in the birthweight standards estimation the parametric method can safely be applied also when the series includes pathologic and preterm newborns.

Birth Weight↗
PubMed1998

Reproducibility of within-subject breath alcohol analysis.

Random samples from normal distributions are an important assumption for many statistical methods. The present study evaluates this assumption with regard to quantitative breath alcohol analyses. Eight individuals (six male and two female) consumed alcoholic beverages and subsequently provided replicate (n ranging from 22 to 69) breath samples to an infrared breath alcohol instrument within short time intervals. The serially collected data were treated with several descriptive and inferential methods. Descriptive results among the eight individuals included: mean 0.0420-0.1175 g/210 L, SD 0.0008-0.0045 g/210 L and CV: 1.9%-4.7%. Statistical tests for normality showed seven of the distributions to be reasonably normal (p > or = 0.25) and the other marginal (p = 0.051). A test for runs about the median showed random results (p > or = 0.10) for four individuals and non-random (p < or = 0.01) for the other four. The results suggest an individual's breath alcohol measurement, when appropriately collected and analysed, should be considered a random sample from a normal within-subject distribution. The existing variability in breath alcohol analysis, due largely to biological and sampling considerations, is acceptably minimized to warrant forensic application.

Adult↗
PubMed2000

Analytical model for the effects of learning on spike count distributions.

The spike count distribution observed when recording from a variety of neurons in many different conditions has a fairly stereotypical shape, with a single mode at zero or close to a low average count, and a long, quasi-exponential tail to high counts. Such a distribution has been suggested to be the direct result of three simple facts: the firing frequency of a typical cortical neuron is close to linear in the summed input current entering the soma, above a threshold; the input current varies on several timescales, both faster and slower than the window used to count spikes; and the input distribution at any timescale can be taken to be approximately normal. The third assumption is violated by associative learning, which generates correlations between the synaptic weight vector on the dendritic tree of a neuron, and the input activity vectors it is repeatedly subject to. We show analytically that for a simple feed-forward model, the normal distribution of the slow components of the input current becomes the sum of two quasi-normal terms. The term important below threshold shifts with learning, while the term important above threshold does not shift but grows in width. These deviations from the standard distribution may be observable in appropriate recording experiments.

Action Potentials↗
PubMed2003

QMLE: fast, robust, and efficient estimation of distribution functions based on quantiles.

Quantile maximum likelihood (QML) is an estimation technique, proposed by Heathcote, Brown, and Mewhort (2002), that provides robust and efficient estimates of distribution parameters, typically for response time data, in sample sizes as small as 40 observations. In view of the computational difficulty inherent in implementing QML, we provide open-source Fortran 90 code that calculates QML estimates for parameters of the ex-Gaussian distribution, as well as standard maximum likelihood estimates. We show that parameter estimates from QML are asymptotically unbiased and normally distributed. Our software provides asymptotically correct standard error and parameter intercorrelation estimates, as well as producing the outputs required for constructing quantile-quantile plots. The code is parallelizable and can easily be modified to estimate parameters from other distributions. Compiled binaries, as well as the source code, example analysis files, and a detailed manual, are available for free on the Internet.

Data Interpretation, Statistical↗
PubMed1999

Joint multipoint linkage analysis of multivariate qualitative and quantitative traits. I. Likelihood formulation and simulation results.

We describe a variance-components method for multipoint linkage analysis that allows joint consideration of a discrete trait and a correlated continuous biological marker (e.g., a disease precursor or associated risk factor) in pedigrees of arbitrary size and complexity. The continuous trait is assumed to be multivariate normally distributed within pedigrees, and the discrete trait is modeled by a threshold process acting on an underlying multivariate normal liability distribution. The liability is allowed to be correlated with the quantitative trait, and the liability and quantitative phenotype may each include covariate effects. Bivariate discrete-continuous observations will be common, but the method easily accommodates qualitative and quantitative phenotypes that are themselves multivariate. Formal likelihood-based tests are described for coincident linkage (i.e., linkage of the traits to distinct quantitative-trait loci [QTLs] that happen to be linked) and pleiotropy (i.e., the same QTL influences both discrete-trait status and the correlated continuous phenotype). The properties of the method are demonstrated by use of simulated data from Genetic Analysis Workshop 10. In a companion paper, the method is applied to data from the Collaborative Study on the Genetics of Alcoholism, in a bivariate linkage analysis of alcoholism diagnoses and P300 amplitude of event-related brain potentials.

Chromosome Mapping↗
PubMed2003

Confidence intervals of Leq in the case of stationary random noise measurements.

A common practice in random noise measurements is to assume that the noise samples are normally distributed. Since the sound pressure level (Lp) is related with the sound energy by a non linear equation, the distribution of the two variables will be different. If one assumes that the probability density function (pdf) of Lp is normal, the pdf of noise energy is not and vice versa. A simple criterion based on statistical properties of sampled noise can be used for the determination of the kind of distribution of the measured noise. The case in which the noise energy emitted by the source, and the case in which the measured noise level is normally distributed are examined. For each case confidence intervals of the calculated equivalent level are calculated.

Confidence Intervals↗
PubMed1974

Observations on the action of type A botulinum toxin on frog neuromuscular junctions.

1. Progressive block of neuromuscular transmission in frog sartorius and gastrocnemius preparations by haemagglutinin-free crystalline Type A botulinum toxin (BTX) was investigated by in vitro application and by injection of the toxin into living animals.2. Neuromuscular block was characterized by (a) decline in amplitude of evoked twitch contractions, (b) decline in amplitudes of end-plate potentials (e.p.p.s) and (c) changes in statistical characteristics of spontaneous miniature end-plate potentials (m.e.p.p.s).3. Progress of the block was enhanced by nerve stimulation.4. A decrease in frequency to less than 0.1/sec and decreased average amplitudes of m.e.p.p.s preceded observable impairment of neuromuscular transmission. These changes occurred as early as 3 hr after injection of the toxin into dorsal lymph sacs.5. The amplitude distributions of m.e.p.p.s changed from a normal distribution to one that showed an increased skewness toward smaller amplitudes as the block progressed. These changes were first detectable as early as 75 min following addition of the toxin to the bath.6. At later stages of toxin action, e.p.p.s began to decrease in amplitude and eventually failed altogether. E.p.p.s showed a normal quantal variation at very early stages in the block in Mg(2+)-treated preparations. At later stages of the block, it was not possible to test the quantal make-up of the e.p.p.7. At all stages before complete failure it was possible to obtain normal or greater than normal degrees of synaptic facilitation with paired stimuli to the nerve. This aspect of the coupling of nerve terminal depolarization to transmitter release appears to be relatively unaffected by BTX.8. Electrical depolarization of nerve terminals in partially blocked preparations evoked a maintained discharge of m.e.p.p.s with an amplitude distribution similar to that of the spontaneous m.e.p.p.s; hyperpolarization of the terminals evokes a distinctly larger class of m.e.p.p.s. In fully blocked preparations, depolarization of the terminals does not evoke transmitter release whereas hyperpolarization continues to yield the larger class of m.e.p.p.s.9. It is proposed that the neuromuscular block caused by BTX is due to impairment of a process by which vesicles become charged with transmitter before release.

Animals↗
PubMed2005

Measures of performance in nonlinear estimation tasks: prediction of estimation performance at low signal-to-noise ratio.

Maximum-likelihood (ML) estimation is an established paradigm for the assessment of imaging system performance in nonlinear quantitation tasks. At high signal-to-noise ratio (SNR), ML estimates are asymptotically Gaussian-distributed, unbiased and efficient, thereby attaining the Cramer-Rao bound (CRB). Therefore, at high SNR the CRB is useful as a predictor of the variance of ML estimates and, consequently, as a basis for measures of estimation performance. At low SNR, however, the achievable parameter variances are often substantially larger than the CRB and the estimates are no longer Gaussian-distributed. These departures imply that inference about the estimates that is based on the CRB and the assumption of a normal distribution will not be valid. We have found previously that for some tasks these effects arise at noise levels considered clinically acceptable. We have derived the mathematical relationship between a new measure, chi2(pdf-ML), and the expected probability density of the ML estimates, and have justified the use of chi2(pdf-ML)-isocontours in parameter space to describe the ML estimates. We validated this approach by simulation experiments using spherical objects imaged with a Gaussian point spread function. The parameters, activity concentration and size, were estimated simultaneously by ML, and variances and covariances calculated over 1000 replications per condition from 3D image volumes and from 2D tomographic projections of the same object. At low SNR, where the CRB is no longer achievable, chi2(pdf-ML)-isocontours provide a robust prediction of the distribution of the ML estimates. At high SNR, the chi2(pdf-ML)-isocontours asymptotically approach the analogous chi2(pdf-F)-contours derived from the Fisher information matrix. The chi2(pdf-ML) model appears to be suitable for characterization of the influence of the noise level and characteristics, the task, and the object on the shape of the probability density of the ML estimates at low SNR. Furthermore, it provides unique insights into the causes of the variability of estimation performance.

Algorithms↗
PubMed1997

p-value adjustments for subgroup analyses.

The analysis of data from clinical trials often includes subgroup analyses, which are performed to examine the treatment effect within various sets of patients based on baseline and/or demographic variables. The goals of these analyses are to establish the consistency of the results across the subgroups and to identify important prognostic factors. The p-values for such analyses are usually presented without any adjustment for the multiple analyses: This approach has been criticized because of the possibility of misleading false positives. Conservative approaches have been proposed to resolve this problem; however, these approaches are usually so conservative that significant results are rarely observed after adjustment. Here an approximate technique for use when the variable of interest has a normal distribution is presented.

Clinical Trials as Topic↗
PubMed1975

The effect of fetal and placental weight at birth on weight during early childhood.

A study of children whose birth weights or placental weights were above the 90th or below the 10th percentile for gestational age indicated that bigness at birth tends to be an innate quality, as the majority of those who were large at birth remained oversized. The small at birth are not all destined to remain diminutive, as the children in this category attained a normal distribution curve for weight during the first year of life. Thus smallness at birth may represent intrauterine nutritional deprivation and be overcome with normal access to calories. The influence of the placenta on infant size is temporary and is modified by extrauterine nutrition. Thus, although there was a direct relationship between birth weight and placental weight, the distribution of weight of children with either large or small placentas was not significantly different from the expected normal distribution at one year of age.

Birth Weight↗
PubMed2006

Reaction time distribution analysis of neuropsychological performance in an ADHD sample.

Differences in reaction time (RT) variability have been documented between children with and without Attention Deficit Hyperactivity Disorder (ADHD). Most previous research has utilized estimates of normal distributions to examine variability. Using a nontraditional approach, the present study evaluated RT distributions on the Conners' Continuous Performance Test in children and adolescents from the Multimodal Treatment Study of ADHD sample compared to a matched sample of normal controls (n = 65 pairs). The ex-Gaussian curve was used to model RT and RT variability. Children with ADHD demonstrated faster RT associated with the normal portion of the curve and a greater proportion of abnormally slow responses associated with the exponential portion of the curve. These results contradict previous interpretation that children with ADHD have slower than normal responding and demonstrate why slower RT is found when estimates of variability assume normal Gaussian distributions. Further, results of this study suggest that the greater number of abnormally long RTs of children with ADHD reflect attentional lapses on some but not all trials.

Attention Deficit Disorder with Hyperactivity↗
PubMedDate not supplied

Norms and sensitivity of the adolescent version of the drug use screening inventory.

The distribution and the statistical accuracy of scores on the Drug Use Screening Inventory (DUSI) and the discriminative power of the DUSI for identifying individuals who qualify for a DSM-III-R diagnosis of Psychoactive Substance Use Disorder (PSUD) were examined in 846 adolescents. The subjects with PSUD had higher mean scores, and the distribution of their scores approximated a normal distribution in each of the 10 domains measured by the DUSI. All of the DUSI domains yielded more precise trait estimates for the subjects who had more severe PSUD. Within the normal sample, using a score of 30 on the overall problem density index as the cutoff score, the DUSI correctly classified 95% of the normal sample and 81% of the PSUD cases.

Adolescent↗
PubMed1993

Distribution of serum lipoprotein(a) levels--a non-parametric analysis.

The distribution of serum lipoprotein(a) [Lp(a)] concentration among Japanese male adults was evaluated using non-parametric methods. The following results were obtained. 1) Among healthy male adults undergoing a medical checkup, Lp(a) showed a highly skewed distribution towards the low level. The distribution could be regarded as a power normal distribution with the power order of 1/2. The median of Lp(a) level was 14.1 mg/dl (the 25th percentile was 6.2 mg/dl and the 75th percentile was 26.7 mg/dl). 2) The values of serum Lp(a) in subjects with vasospastic angina distributed at a higher level than for subjects with normal coronary arteries as diagnosed by coronary angiography. 3) The observed serum Lp(a) concentration moved to a higher range as the number of branches with significant stenosis on the coronary angiography increased. 4) Serum Lp(a) was one of the risk factors for ischemic heart disease. Its odds ratio when the cut-off value was set at 26.7 mg/dl or 30 mg/dl was 2.52 and 2.94, respectively. Information on the distribution of serum Lp(a) concentration is useful for estimating the coronary atherogenic factor.

Adult↗