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PubMed1993

Converting Tanner-Whitehouse reference tricep and subscapular skinfold measurements to standard deviation scores.

The use of conventional standard deviation (SD) scores is inappropriate when data are not normally distributed, as is the case with the tricep and subscapular skinfolds. However, it is now possible to summarize centile data in three age-specific parameters (called L, M and S) and by the appropriate use of these parameters, SD scores for skinfold measurements can be calculated that take into account skewness in the centile data. The L, M and S parameters for the tricep and subscapular skinfolds from age 1 to 19 years [J. M. Tanner & R. H. Whitehouse (1975) Arch. Dis. Childh. 50, 142-145] are presented and the equation for the calculation of SD scores described.

Adolescent↗

PubMed2004

Significance of consecutive international normalized ratio (INR) outcomes using statistical control rules in long-term anticoagulated patients. Optimization of laboratory monitoring and interpretation of borderline measurements.

Analysis of serial measurements is needed to elaborate observations in all fields of medical research. In the present study, retrospective data of anticoagulated patients were used to calculate a mean of observations and control limits, X+/-1sigma and X+/-2sigma (mean+/-standard deviation). During 18 months of coagulation monitoring, 45 patients without major oral anticoagulant therapy complications, with more international normalized ratio (INR) determinations in the therapeutic range and with a normal distribution of INR values according to the Kurtosis coefficient, were selected. The cumulative distribution functions allowed us to obtain critical limits of INR with a cumulative probability (p). Control limits, calculated for a therapeutic control chart, indicated through different control rules, 1S2 or 2S1, an alarm signal to analyze the cause of INR outside the therapeutic range. Our investigation suggested that for results at the level of the therapeutic control limits, we needed at least two consecutive INR results to detect a significant over- or under-anticoagulation. The therapeutic control chart method should be a useful means in clinical practice for evaluating the statistical significance of consecutive and borderline INR outcomes. Analytical improvements and control rules applied to laboratory monitoring may help optimize drug dose administration.

Algorithms↗

PubMed1997

Removable surface contamination at a biomedical research institution.

A rigorous, unannounced, campus-wide survey for removable surface contamination was performed at our institution. Wipe samples (n = 1,090) were collected from a variety of standardized locations in 45 large biomedical research laboratories that routinely use kBq-MBq (microCi-mCi) amounts of 3H, 14C, 32P, 35S, 51Cr, and 125I. The results showed a log-normal distribution for contamination, with about 90% of all samples below ten times background. Although working surfaces and equipment used in these laboratories can become contaminated with radioactive materials, especially by transfer from soiled gloves, the magnitude of the contamination is very small and typically restricted to surfaces, instruments, and equipment that are directly handled in the course of experimental work and which can be reasonably anticipated to be contaminated. These data suggest that contamination is not a significant problem in biomedical research laboratories at this institution and that the best protection from workplace contamination appears to continue to be the use of well-reviewed standard operating procedures and good work practices.

Carbon Radioisotopes↗

PubMed2005

Assessment of reference values for selected elements in a healthy urban population.

Reference values for 26 elements, namely Al, Ba, Be, Bi, Ca, Cd, Co, Cr, Cu, Fe, Hg, Li, Mg, Mn, Mo, Ni, Pb, Sb, Si, Sn, Sr, Tl, V, W, Zn and Zr are proposed in serum and blood of 110 healthy adults of the urban area of Rome. They were included in the study on the basis of strict criteria of eligibility and exclusion. With the exception of Ba, Bi, Co, Cr, Ni, Sb, Sn Tl in serum, and Bi, Hg, Si, V and W in whole blood, experimental data for each all the other analytes were found to approach a normal distribution. The estimated 5-95% references ranges (in ng ml(-1)) were reported. For several elements the reference ranges observed overlapped information available in the literature. Gender, age, body mass index, smoking habits and alcohol consume were used as grouping variables. Mutual associations were observed for several elements, as follows: Be, Ca, Co, Cr, Cu, Li, Mo, Pb and Zn with sex; Ca, Pb and Si with age (< and > 45 years); Co, Cr, Mo, Sb and Tl with body mass index; Cd and Pb with smoking habit; Cr and Pb with alcohol consume.

Adult↗

PubMed2000

Estimation of individual genetic effects from binary observations on relatives applied to a family history of respiratory illnesses and chronic lung disease of newborns.

This paper considers methods for estimating the relationship between a binary response Y and the genetic effects responsible for a second binary trait Z. The responses Y are observed only for target individuals, and the responses Z are observed only for the relatives of these targets. The analysis consists of two parts. The first part concerns the analysis of the family data Z and the second part estimates the relation between the genetic effects and Y. For the family data, a generalized linear mixed model with a logit link and Gaussian genetic (random) effects is used. Estimates of the variances of the genetic effects are obtained by using a pseudo-profile log-likelihood method. Estimation of the log likelihood involves averaging over n-dimensional normal distributions, which is done by importance sampling. The methods used in the second part are straightforward. The methods are applied to a data set containing chronic lung disease (CLDN) responses of newborns and asthma (AS), allergy (AL), chronic bronchitis (CB) and eczema (EC) responses observed for the relatives of these newborns. The clinical question is whether genetic effects of AS, AL, CB, and EC have an effect on the risk for CLDN. It can be concluded that for AS, AL, CB, and EC, the influence of genetic effects is significant. However, these genetic predispositions have no significant effect on CLDN.

Asthma↗

PubMed1989

Distribution of adenosine deaminase complexing protein (ADCP) in human tissues.

The normal distribution of adenosine deaminase complexing protein (ADCP) in the human body was investigated quantitatively by ADCP-specific radioimmunoassay (RIA) and qualitatively by immunohistochemistry. In these studies we used a specific rabbit anti-human ADCP antiserum. In all 19 investigated tissues, except erythrocytes, ADCP was found by RIA in the soluble and membrane fractions. From all tissues the membrane fractions contained more ADCP (expressed per mg protein) than the soluble fractions. High membrane ADCP concentrations were found in skin, renal cortex, gastrointestinal tract, and prostate. Immunoperoxidase staining confirmed the predominant membrane-associated localization of the protein. In serous sweat glands, convoluted tubules of renal cortex, bile canaliculi, gastrointestinal tract, lung, pancreas, prostate gland, salivary gland, gallbladder, mammary gland, and uterus, ADCP immunoreactivity was found confined to the luminal membranes of the epithelial cells. These data demonstrate that ADCP is present predominantly in exocrine glands and absorptive epithelia. The localization of ADCP at the secretory or absorptive apex of the cells suggests that the function of ADCP is related to the secretory and/or absorptive process.

Adenosine Deaminase↗

PubMed2004

Temporal order of nonlinear dynamics in human brain.

In previous spectral analysis investigations, we demonstrated that the spontaneous activity of the alpha EEG is not stationary but rather shows cyclic alterations with a circa 1-min periodicity. Following the conclusion that a power increase in the alpha band implies a neuronal synchronization, and vice versa, an associated decrease of the EEG complexity was postulated. Accordingly, a rhythmic variation, i.e., a temporal order of the nonlinear dynamics with similar period length, was expected. Bipolar 4-min EEG recordings were obtained from 20 awake subjects (mean age: 23.5+/-2.5 years) with eyes closed for the EEG leads C3, C4, Oz, and Fz according to the 10-20 system. For the automatic evaluation of spontaneous alterations of complexity, a sliding computation of the so-called correlation dimension, using an analysis window length of 20 s continuously shifted by 1 s, was performed. The time series of complexity exhibited an oscillatory behavior with a mean period length of 58.7 s; the Friedman test statistic revealed no significant topological differences. For the rejection of the null hypothesis that the observed periodicity is a random one, two-group t-tests and ANOVA with repeated measures were performed, comparing the corresponding amplitudes and period lengths with those derived from 20 pseudo-random signals (taken from a multivariate Gaussian normal distribution). The mean relative change of EEG complexity was highly significantly increased (P<0.0001) compared to that of random data. Likewise, the difference of mean period lengths was also significant (P<0.01). The results indicate that the coupling strength of the neural network of the brain changes periodically, with a cyclic alteration from a central to a parallel processing mode of information, reflecting state transitions from synchronized, low-complex EEG activity to desynchronized high-complex activity, and vice versa. Various neuronal control mechanisms that may be acting as pacemakers responsible for the temporal order of such transients are discussed. A disturbance of the temporal order may be of pathophysiological significance.

Action Potentials↗

PubMed2000

Analysis of the feeding behavior of pigs using different models.

Short-term feeding behavior is conventionally analysed using random process models. The assumption underlying these models have recently been questioned and this article describes the application of both random, and more biologically based, models to the feeding behavior of pigs. Feeder visits of 16 growing pigs, housed individually from 17 to 52 kg live weight, were recorded electronically over a continuous period of 35 days. Daily food intake increased linearly with time, but there was considerable individuality in the degree of order. Pigs made between 18.8 and 80.3 (mean 47.9) daily visits to the feeder. Intervals between visits could be described by two log-normal distributions. Two Gaussian density functions were fitted to the distribution of the log-transformed intervals. For the combined data from all animals the within- and between-meal intervals were 11.2 s and 100.1 min, respectively. A model with three Gaussian functions gave an improved fit to the interval distribution. The within and between meal intervals were then estimated to be 4.2 s and 93.9 min, respectively. The middle distribution of intervals ranged from 0.5 to 38.1 min. The intervals were also described by random process models; again, a three-process model gave an improved fit compared to a two-process model. The mean estimated number of meals per day from the three Gaussian model was 14.3, and from the three process random model, 16.3. A biological interpretation of the three types of interval suggests that: (1) pigs eat in meals separated by long intervals; (2) meals consist of clusters of eating bouts separated by shorter intervals, sometimes associated with drinking; (3) within each eating bout short intervals occur as pigs constantly move in and out of the feeder. It remains unclear what underlies the observed patterns of eating.

Animals↗

PubMed2002

Exact and approximate Bayesian estimation of net counting rates.

The stochastic fluctuations in the number of disintegrations, which had already been studied experimentally by Rutherford and other investigators at the beginning of the twentieth century, make estimation of net counting rates in the presence of background counts a challenging statistical problem. Exact and approximate Bayesian estimates of net count rates using Poisson and normal distributions for the number of counts detected during varying counting intervals are derived. The posterior densities for the net count rate are derived and plotted for uniform priors. The graphs for the exact, Poisson based, and for the approximate posterior densities of the background and net count rates, resulting from the normal approximation to the Poisson distribution, were compared. No practical differences were found when the number of observed gross counts is large. Small numerical differences in the posterior expectations and standard deviations of the counting rates appeared when the number of observed counts was small. A table showing some of these numerical differences for different background and gross counts is included. A normal approximation to the Poisson is satisfactory for the analysis of counting data when the number of observed counts is large. Some caution has to be exercised when the number of observed counts is small.

Artifacts↗

PubMed1992

[The correlations of somatotypes and the total ridge count in Russian men of the White Sea area].

Under investigation there were 158 Russian men of the city of Arkhangelsk and Arkhangelsk Province aged from 18 to 30 years. The total ridge count (TRC) and indices of the body constitution (according to V. M. Shevkunenko--A. M. Geselevich) were studied: relative length of the trunk (RLT), relative length of lower extremities, relative width of the shoulders and relative width of the pelvis. The hypothesis of normal distribution of these indices was confirmed by the chi-square criterion. The division into groups of dolicho- (DS), meso- and brachymorphic somatotypes (BS) was performed according to each sign and with special reference to limits X+/-S. Comparison of people of BS and DS groups has revealed significant differences only for RLT. The correlation coefficient proved to be valuable exceptionally for RLT. The method of succession analysis has shown that the least amount of observations for the determination of significant differences according to TRC is required in somatotyping according to RLT. Further investigations with other parameters of somatotyping require considerable amount of observations. The correlation analysis has determined the significant correlation coefficient for RLT only. A conclusion is made of the correlation of finger patterns and TRC with the rate of growing processes of organism.

Adolescent↗

PubMed1989

A method for assessing the statistical significance of RNA folding.

We have developed a statistical method that is designed for analyzing potential RNA folded substructures. The statistical significance of RNA folding is assessed by the segment score. The segment score is defined as the difference between the lowest free energy calculated for the real biological sequence and the mean of the lowest free energies from random permutations of the real segment sequence, divided by the standard deviation of the random sample. This procedure was applied to the well-studied Escherichia coli 16S rRNA and potato spindle tuber viroid (PSTV) RNA. The results showed that the predictions of the locally significant secondary structures in these two molecules are in accord with the universally conserved local secondary structure elements (Gutell, Weiser & Noller, 1985, Prog. Nucl. Acid Res. molec. Biol. 32, 155-216; Riesner & Gross, 1985, A. Rev. Biochem. 54, 531-564). In addition, a statistical analysis indicated that the lowest free energies of a random sample set follow an approximately normal distribution. A reasonable size for the random sample set was determined statistically. Moreover, the statistical evaluation has been carried out using three different sets of energy rules--two sets (Salser, 1977, Cold Spring Harb. Symp. Quant Biol. 42, 985-1002; Freier, Kierzek, Jaeger, Sugimoto, Caruthers, Neilson & Turner, 1986, Proc. natn. Acad. Sci. U.S.A. 83, 9373-9377) take into account stacking energies and are based on experimental data and their computational extension (Salser, 1977)--the third set is a simplistic "unitary matrix" approach, where any base-pair is given a weight of "minus one" and an unpaired based is "zero". The Freier energy rules usually yield the strongest indication of significant folding region. However, the results derived from paired comparisons test don't provide sufficient evidence for concluding that a different set of energy rules is effective in changing the segment score level for local stem-loop structures in the 16S rRNA.

Analysis of Variance↗

PubMed1994

Sibling correlations and segregation analysis of age-related maculopathy: the Beaver Dam Eye Study.

Sibling correlations were evaluated and segregation analysis was performed on age-dependent maculopathy scores of the right and left eyes of individuals from 564 families in the Beaver Dam Eye study. There is evidence of significant sibling correlations. The data fit a mixture of two normal distributions, especially after undergoing the Box and Cox power transformation. In each eye, the hypothesis of mendelian transmission of a major effect cannot be rejected under the tau AB free model, but is rejected under the tau's free model. The hypothesis of a random environmental major effect is rejected. Similar major gene parameter estimates are found for both eyes. The results are consistent with a major effect accounting for 62% and 59%, in the right and left eyes, respectively, of the determination of age-related maculopathy scores. A single major gene can account for about 89% and 97% of this variability due to a major effect, or for about 55% and 57% of the total variability, in the right and left eyes, respectively.

Adult↗

PubMed2006

Likelihood ratio, optimal decision rules, and correct response probabilities in a signal detection theoretic, equal-variance Gaussian model of the observer in the 4IAX paradigm.

This article provides a synthetic account of the likelihood ratio, optimal decision rules, and correct response probabilities in a signal detection theoretic model of the observer in the dual-pair comparison, or four-interval AX (4IAX), paradigm. The model assumes a static sampling process, resulting in four, equal-variance normally distributed (i.e., Gaussian) observations on each trial First, a likelihood ratio equation allowing for an arbitrary degree of correlation between observations is provided. Specific solutions for the cases of independent and highly correlated observations are then derived. It is shown that these solutions, and the associated decision rules, correspond to those provided independently in earlier publications. A modified 4IAX paradigm involving, as a standard, an additional stimulus (C) located medially between the A and the B stimuli is also considered. It is shown that the optimal (static, equal-variance, Gaussian) decision model for this paradigm is unaffected by correlation between observations and is equivalent to the standard 4IAX with highly correlated observations. Finally, we consider how, under the considered (static, equal-variance, Gaussian) model, the proportion of correct responses in the different versions of the 4IAX paradigm is related to d', and a solution for the case of independent observations is provided.

Decision Making↗

PubMed1998

A comparison of estimates of the prevalence of heavy drinkers in local regions of Queensland.

OBJECTIVE: This study developed and compared separate estimates of the number of heavy drinkers (the in-need population for alcohol treatment interventions) across eight local regions in Queensland. METHOD: Estimates were based on: (i) a self-report population survey of alcohol consumption; and (ii) an application of the Ledermann log-normal distribution of consumption model to liquor sale figures. RESULTS: Estimates based on the 1989-1990 National Health Survey (NHS) data indicated that 10.98% (n = 83,880) of adult male drinkers and 1.25% (n = 6581) of adult female drinkers in Queensland (total = 90,461) were on average drinking the equivalent of six or more standard drinks a day in the week prior to the survey (4.74% of Queensland adult drinkers, n = 90,461). Estimates based on the Ledermann model indicated that 12.18% of adult Queensland drinkers (n = 232,283) were drinking six or more standard drinks a day. Estimates based on the Ledermann model were 157% larger than estimates based on NHS data (i.e. a difference of 141,821 heavy drinkers), with large variations in the two estimates across local regions. CONCLUSION: The NHS data appears to underestimate the population of heavy drinkers, whereas the Ledermann model overestimates it. In this situation, it seems preferable to use the more conservative self-report survey estimates.

Adolescent↗

PubMed2002

Histologic and radiographic assessment of caries-like lesions localized at the crown margin.

STATEMENT OF PROBLEMS: Little is known about the impact of crown margins on the demineralization and remineralization process or on the interpretation of radiographs for the detection of early secondary caries. PURPOSE: The aim of this study was to correlate the findings from 2 different radiographic techniques with the results of a histologic assessment of carieslike lesions at the crown margin. MATERIAL AND METHODS: Ten fully impacted third molars were extracted and restored with complete metal crowns with chamfer preparations. For each tooth, the prepared margin ended in enamel on one side and extended into cementum/dentin on the other. After being thoroughly cleaned, the teeth were covered with wax except for a 2- x 3-mm window at the crown margin in each of 2 test areas localized at the interproximal enamel and cementum/dentin junction. During demineralization with 6% hydroxyethyl cellulose gel at pH 4.9, direct digital radiographs or conventional radiographs were made at baseline and after 7, 14, 21, and 28 days. Each radiograph was blinded and examined for the presence/absence of lesions by 3 calibrated observers who used predetermined criteria required for receiver operating characteristic (ROC) analysis. After 28 days, the teeth were imbibed with methyl methacrylate and serially ground sectioned for assessment of the lesions in polarized light. Morphometric analysis of lesion extension included the calculation of mean values and standard deviations. Kappa and ROC analysis were applied to assess radiographs made at different demineralization time periods, localization of the crown margins in enamel or cementum/dentin, and direct digital and conventional radiographs. Data were tested for normal distribution (QQ plot), and statistical differences were calculated with Tukey's honestly significant difference post hoc test. RESULTS: Radiographic evaluation revealed only slight interexaminer agreement (Kappa) for enamel lesions (direct digital 0.19, conventional radiographs 0.2) and a fair interexaminer agreement for cementum/dentin lesions (direct digital 0.35, conventional radiographs 0.33). ROC analysis revealed no differences between the radiographic techniques. Lesions localized in cementum/dentin (direct digital 0.86 +/- 0.14, conventional radiographs 0.86 +/- 0.09) were diagnosed more reliably than those in enamel (direct digital 0.79 +/- 0.05, conventional radiographs 0.72 +/- 0.10). As microscopically assessed, the depth of lesions in enamel was less than that of lesions in cementum/dentin (49.3 +/- 7.3 microm vs 89.5 +/- 13.2 microm). Erosions were found in cementum/dentin (depth 25.2 +/- 5.3 microm). CONCLUSION: Within the limitations of this study, small artificial lesions were detected equally well by conventional and direct digital radiography. However, because of low interexaminer agreement, the radiographic assessment did not reproduce true histopathologic lesion characteristics documented by morphometry of serial ground sections.

Adolescent↗

PubMed1983

The normal and abnormal distribution of the adrenomedullary imaging agent m-[I-131]iodobenzylguanidine (I-131 MIBG) in man: evaluation by scintigraphy.

The scintigraphic distribution of m-[131I]iodobenzylguanidine (I-131 MIBG), an adrenal medullary imaging agent, was studied to determine the patterns of uptake of this agent in man. The normal distribution of I-131 MIBG includes clear portrayal of the salivary glands, liver, spleen, and urinary bladder. The heart, middle and lower lung zones, and colon were less frequently or less clearly seen. The upper lung zones and kidneys were seldom visualized. The thyroid appeared only in cases of inadequate thyroidal blockade. The "normal" adrenal glands were seldom seen and faintly imaged in 2% at 24 hr after injection and in 16% at 48 hr, in patients shown not to have pheochromocytomas, whereas intra-adrenal, extraadrenal, and malignant pheochromocytomas usually appeared as intense focal areas of I-131 MIBG uptake at 24 through 72 hr.

3-Iodobenzylguanidine↗

PubMed2006

Application of public-domain statistical analysis software for evaluation and comparison of comet assay data.

A novel approach for statistical analysis of comet assay data (i.e.: tail moment) is proposed, employing public-domain statistical software, the R system. The analytical strategy takes into account that the distribution of comet assay data, like the tail moment, is usually skewed and do not follow a normal distribution. Probability distributions used to model comet assay data included: the Weibull, the exponential, the logistic, the normal, the log normal and log-logistic distribution. In this approach it was also considered that heterogeneity observed among experimental units is a random feature of the comet assay data. This statistical model can be characterized with a location parameter m(ij), a scale parameter r and a between experimental units variability parameter theta. In the logarithmic scale, the parameter m(ij) depends additively on treatment and random effects, as follows: log(m(ij)) = a0 + a1x(ij) + b(i), where exp(a0) represents approximately the mean value of the control group, exp(a1) can be interpreted as the relative risk of damage with respect to the control group, x(ij) is an indicator of experimental group and exp(b(i)) is the individual risk effects assume to follows a Gamma distribution with mean 1 and variance theta. Model selection is based on Akaike's information criteria (AIC). Real data coming from comet analysis of blood samples taken from the flounder Paralichtys orbignyanus (Teleostei: Paralichtyidae) and from samples of cells suspension obtained from the estuarine polychaeta Laeonereis acuta (Nereididae) were employed. This statistical approach showed that the comet assay data should be analyzed under a modeling framework that take into account the important features of these measurements. Model selection and heterogeneity between experimental units play central points in the analysis of these data.

Animals↗

PubMed2004

The sampling distributions of Gaussian ROC statistics.

For a discrimination experiment, a plot of the hit rate against the false-alarm rate--the ROC curve--summarizes performance across a range of confidence levels. In many content areas, ROCs are well described by a normal-distribution model and the z-transformed hit and false-alarm rates are approximately linearly related. We examined the sampling distributions of three parameters of this model when applied to a ratings procedure: the area under the ROC (Az), the normalized difference between the means of the underlying signal and noise distributions (da), and the slope of the ROC on z-coordinates (s). Statistical bias (the degree to which the mean of the sampling distribution differed from the true value) was trivial for Az, small but noticeable for da, and substantial for s. Variability of the sampling distributions decreased with the number of trials and was also affected by the number of response categories available to the participant and by the overall sensitivity level. Figures in the article and tables available on line can be used to construct confidence intervals around ROC statistics and to test statistical hypotheses.

Humans↗