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PubMed1987

[Effect of new imaging procedures on conventional roentgen diagnostic methods].

The diagnostic radiology workload of a general hospital served as basis to assess the statistical distribution of various diagnostic radiology methods and the inroads made by new imaging methods on the conventional ones: CT, DAS, sonography and endoscopy. In particular, the statistical breakdown shows how these methods have been applied in examining the gastrointestinal tract, the kidneys, the gallbladder and biliary tract, and how they have influenced the frequency rate of special examination methods such as angiography and myelography. Statistic assessment of the results obtained during the past ten years shows an increasing predominance of less invasive examination methods and increasing use of endoscopic methods for examining the gastrointestinal tract, the sum total of examinations remaining approximately the same throughout.

Angiography↗

PubMed1988

Applications of statistical analysis in diagnostic histopathology and cytopathology.

Corresponding to the rapid increase in the amount of data available for use in clinical diagnoses, there is an increased need for procedures that can provide the diagnostician with meaningful statistical summaries of data and with statements concerning the statistical significance associated with a diagnostic evaluation. It has been demonstrated that multivariate statistical assessment of clinical material can provide consistent, reliable and highly sensitive diagnostic clues, even in instances in which trained personnel are unable to see any change. Several examples of applications of statistical analyses in diagnostic cytology and histopathology are given in this paper. The examples were chosen to be illustrative of the different types of problems for which statistical analyses have been found useful. These problems differ with respect to the extent of the statistical methods thus far developed and the difficulty involved in developing further analyses. For many problems, appropriate statistical analyses are readily available; other problems require definition of custom-made test statistics and, in some cases, also definition of new statistical distributions. The problems discussed here are only a small sample of the existing problems, but they provide at least an indication of the scope of the role that statistics plays in cytopathologic and histopathologic diagnosis.

Cytological Techniques↗

PubMed1986

Normative and reliability data for the Children's Depression Inventory.

The present study was undertaken to examine some of the psychometric properties of the Children's Depression Inventory (CDI), a self-report inventory devised by Kovacs and Beck (1977) to measure depression in children and adolescents. Normative and reliability data were obtained from three independent samples taken from eight public schools in central Pennsylvania. Age- and gender-related differences in reported characteristics of depression were also investigated. The subjects were 594 males and 658 females whose ages ranged from 8 to 16 years and whose combined mean age was 11.67 years (SD = 1.91). The CDI was group-administered to all 1,252 subjects; 155 fifth-grade subjects (77 males and 78 females) were retested after 3 weeks, and 107 seventh- and eight-grade subjects (45 males and 62 females) were retested after 1 year. The distribution statistics for the combined samples yielded an overall CDI mean of 9.09, a standard deviation of 7.04, and a cutoff score of 19 for the upper 10% of the distribution. Reliability assessed through coefficient alpha, item-total score product-moment correlations, and test-retest coefficients proved acceptable. Gender differences were obtained for several item-total score correlations and for test-retest reliability of CDI scores.

Adolescent↗

PubMed1979

Areawide fluctuations in hospital daily census.

The importance of variations in hospital census for planning bed requirements has long been recognized. Traditional models assume Poisson or normal distribution patterns accurately describe such variations in specific hospital units, entire facilities, and groups of hospitals serving the same area. A study of 20 groups of hospitals in five states indicates that these traditional statistical distributions are only occasionally accurate. Different services display different census variation patterns. The standard deviation of the daily census distribution becomes increasingly higher than the square root of the mean estimate as the size of the mean increases. Implications of this finding for regional planning and coordination of hospitals are discussed.

Bed Occupancy↗

PubMed1980

Influence of analytical quality on the diagnostic power of a single S-CK B test in patients with suspected acute myocardial infarction.

We have compared tow theoretical methods for assessing the effects of changing analytical quality of a clinical chemical test. The test considered was S-creatine kinase B subunit activity, used as the only diagnostic criterion for acute myocardial infarction. The two methods applied were based on (i) graphical analysis, and (ii) computer simulation. The results comprise the effects of changing analytical imprecision and bias on the weighted sum of misclassified cases on basis of the test results. The two methods yield comparable results at high analytical imprecision, but due to differences in assumptions about the error distribution of test results the difference increases with increased analytical imprecision. The graphical analysis is easily performed but is restricted in possible applications. The computer simulation is not a generally available methodology, but allows for mixing of different types of statistical distributions, which is not the case in conventional variance analysis.

Chemistry Techniques, Analytical↗

PubMed1987

Nasal resistance to airflow (its measurement, reproducibility and normal parameters).

A method of rhinomanometry is described for use in clinical research work. The statistical distribution of nasal resistance values is studied in a sample of 59 normal individuals. The variation of nasal resistance within two individuals is studied over a period of 7 hours. The choice of appropriate statistical tests to be used when comparing nasal resistance values is discussed. The reproducibility of nasal resistance measurements is assessed in 47 normal individuals. The results were used to define a normal range of values for total nasal resistance to airflow.

Adolescent↗

PubMed1990

Changes in the distribution of ventricular ectopic beats in long-term electrocardiograms.

Only simple methods have been used to assess antiarrhythmic and proarrhythmic effects when comparing baseline and on-therapy Holter recordings taken from the same patient. The paper suggests a new method for definition of these effects based upon comparisons of statistical distributions of ectopic beats. The method is based on multiple random sampling of the recordings and on application of the Smirnov test to compare the samplings. The results of these multiple comparisons are subsequently evaluated using the chi-squared test. An analysis is reported of Holter recordings made on seven patients suffering from ventricular arrhythmia but with anatomically normal heart. In each patient, one baseline recording and one recording on each of three different drugs were made. The results show that the definition of proarrhythmic effects can be partly addressed in a precise mathematical way. The method can also detect a significant change in the character of arrhythmia which can neither be classified as antiarrhythmic nor as proarrhythmic.

Arrhythmias, Cardiac↗

PubMed1984

GalNAc/Gal-specific rat liver lectins: their role in cellular recognition.

By investigating the presence and distribution of GalNAc/Gal-specific receptors on liver cells in vitro and in vivo, we provided evidence that the hepatocyte is not the only liver cell expressing receptor activity but that receptors of similar specificity are found on liver macrophages and also on endothelial cells. The receptor distribution in the plasma membrane is strinkingly different between the three cell types, as judged from the binding pattern of colloidal gold particles coated with asialofetuin or lactosylated serum albumin. Binding to hepatocytes occurs as single particles statistically distributed, binding to liver macrophages in a clustered arrangement all over the cell membrane and binding to endothelial cells also in a clustered arrangement but restricted to coated pits only. The different receptor distribution results in different binding and uptake abilities. Whereas hepatocytes bind and take up molecules and small particles (5 nm) only, the clustered receptor arrangement of endothelial cells and macrophages enables them to effectively bind and ingest larger particles. Ligands larger than 35 nm can be taken up by the macrophages only. The different receptor arrangement results also in different capacities of cell contact formation. Although in vitro liver macrophages and hepatocytes can both bind desialylated cells the macrophage needs much less galactosyl groups exposed on erythrocytes to establish stable contacts than the hepatocyte. The contacts formed by hepatocytes stay reversible for 30 min at 37 degrees C, whereas the contacts formed by the liver macrophages become irreversible after 10 min at 37 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1976

Particle size-shape distributions: the general spheroid problem. I. Mathematical model.

The development of stereological methods for the study of dilute phases of particles, voids or organelles embedded in a matrix, from measurements made on plane or linear intercepts through the aggregate, has deserved a great deal of effort. With almost no exception, the problem of describing the particulate phase is reduced to that of identifying the statistical distribution--histogram in practice--of a relevant size parameter, with the previous assumption that the particles are modelled by geometrical objects of a constant shape (e.g. spheres). Therefore, particles exhibiting a random variation about a given type of shape as well as a random variation in size, escape previous analyses. Such is the case of unequiaxed particles modelled by triaxial ellipsoids of variable size and eccentricity parameters. It has been conjectured (Moran, 1972) that this problem is indetermined in its generally (i.e. the elliptical sections do not furnish a sufficient information which permits a complete description of the ellipsoids). A proof of this conjecture is given in the Appendix. When the ellipsoids are biaxial (spheroids) and of the same type (prolate or oblate), the problem is identifiable. Previous attempts to solve it assume statistical independence between size and shape. A complete, theoretical solution of the spheroids problem--with the independence condition relaxed--is presented. A number of exact relationships--some of them of a striking simplicity--linking particle properties (e.g. mean-mean caliper length, mean axial ratio, correlation coefficient between principal diameters, etc.) on the one hand, with the major and minor dimensions of the ellipses of section on the other, emerge, and natural, consistent estimators of the mentioned properties are made easily accessible for practical computation. Finally, the scope and limitations of the mathematical model are discussed.

Mathematics↗

PubMed1990

A comparison of multivariable mathematical methods for predicting survival--I. Introduction, rationale, and general strategy.

This paper and the two following papers (Parts I-III) report an investigation of performance variability for four multivariable methods: discriminant function analysis, and linear, logistic, and Cox regression. Each method was examined for its performance in using the same independent variables to develop predictive models for survival of a large cohort of patients with lung cancer. The cogent biologic attributes of the patients had previously been divided into five ordinal stages having a strong prognostic gradient. With stratified random sampling, we prepared seven "generating" sets of data in which the five biologic stages were arranged in proportional, uniform, symmetrical unimodal, decreasing exponential, increasing exponential, U-shaped, or bi-modal distributions. Each of the multivariable methods was applied to each of the seven generating distributions, and the results were tested in a separate "challenge" set, which had not been included in any of the generating sets. The research was intended not merely to compare the performance of the multivariable methods, but also to see how their performance would be affected by different statistical distributions of the same cogent biologic attributes. The results, which are presented in the second and third papers, were compared for selection of independent variables and coefficients, and for accuracy in fitting the generating sets and the challenge set.

Cohort Studies↗

PubMed1992

Mass isotopomer distribution analysis: a technique for measuring biosynthesis and turnover of polymers.

Mass isotopomer distribution analysis (MIDA) is a technique for measuring biosynthesis and turnover of polymers in vivo. A stable isotopically enriched precursor is administered, and the relative abundances of different mass isotopomers in the polymer of interest are measured by mass spectrometry (MS). By comparison of statistical distributions predicted from the binomial or multinomial expansion to the pattern of excess isotopomer frequencies observed in the polymer, the enrichment of the biosynthetic precursor subunits (p) for newly synthesized polymers is calculated. MIDA thereby provides a solution to the problem of determining the isotope content in the actual precursor molecules that entered a particular polymeric product (the "true" precursor). The fraction of polymer molecules in a mixture that were newly synthesized during an isotopic experiment (fractional synthesis) can then be calculated. We describe some mathematical characteristics of MIDA and point out certain advantageous features. For example, mathematical estimates of p remain valid even if there does not exist a single anatomic or functional precursor pool. The interpretation of decay curves of endogenously labeled polymers may be improved by the use of higher mass isotopomers, which better fulfill the assumption of flash labeling. By combining fractional synthesis values with rate constants of decay, absolute endogenous synthesis rates can be calculated. Thus, by using probability logic combined with MS analysis, MIDA allows dynamic measurements to be made through analyses on a polymer alone during both isotopic incorporation and decay phases. The method has been applied to fatty acids, cholesterol, and glucose and is potentially applicable to nucleic acids, porphyrins, perhaps proteins, and many other classes of polymers.

Indicator Dilution Techniques↗

PubMed1977

Two-dimensional probabilistic images discrimination. I. Simultaneously presented pairs of patterns.

Reaction time and judgment of similarity or dissimilarity were studied in an experiment on two-dimensional probabilistic images (TDPIs) composed of rectangular black and white cells with statistical distribution of these elements 0.5-0.5. The subjects were asked to report verbally whether pairs of TDPIs, presented for 700 ms, appeared to them similar or not. Three sets of TDPIs differed as to the size of their "grain". Within the pairs "physically identical patterns", "statistically same patterns" or "different patterns" have been used. The statistically same patterns pairs reached the lowest (39 percent) judgment correctness. Reaction times for these pairs were generally longer than for others. In the case of identical patterns and statistically same patterns pairs the results indicated a general increase of the processing time as the size of grain had increased. There was a general tendency of reaction time shortening in successive sessions. These results suggest that correct discrimination of TDPIs does not depend primarily upon their grain.

Adult↗

PubMed1980

Development and distribution of proximal caries in 303 9-20-year-old individuals in a Copenhagen suburb.

The purpose of the present study was to establish a theoretical basis for the practice of screening for identification of caries risk groups. Longitudinal data concerning the development of proximal caries in 303 persons from the age of 9 to the age of 20 were examined with regard to statistical distribution. Data from each year and from the entire period showed a close fit to the negative binomial distribution. This distribution can be the result of independent random occurrences, but varying susceptibility. Thus the consistent existence of a caries risk group is illustrated by this analysis, but no prediction is made. It is suggested that future evaluations of preventive measure directed toward caries risk groups should express the degree to which the similarity between the distribution of proximal caries and the negative binomial distribution can be eliminated.

Adolescent↗

PubMed1992

The effect of neglecting correlations when propagating uncertainty and estimating the population distribution of risk.

Interest in examining both the uncertainty and variability in environmental health risk assessments has led to increased use of methods for propagating uncertainty. While a variety of approaches have been described, the advent of both powerful personal computers and commercially available simulation software have led to increased use of Monte Carlo simulation. Although most analysts and regulators are encouraged by these developments, some are concerned that Monte Carlo analysis is being applied uncritically. The validity of any analysis is contingent on the validity of the inputs to the analysis. In the propagation of uncertainty or variability, it is essential that the statistical distribution of input variables are properly specified. Furthermore, any dependencies among the input variables must be considered in the analysis. In light of the potential difficulty in specifying dependencies among input variables, it is useful to consider whether there exist rules of thumb as to when correlations can be safely ignored (i.e., when little overall precision is gained by an additional effort to improve upon an estimation of correlation). We make use of well-known error propagation formulas to develop expressions intended to aid the analyst in situations wherein normally and lognormally distributed variables are linearly correlated.

Analysis of Variance↗

PubMed1991

Distribution of time to first postpartum estrus in beef cattle.

The function of a distribution that describes postpartum interval (PPI) under any experimental treatment is useful for simulation modeling, understanding the effects of stimuli on the endocrine system, and estimating the average PPI in experiments terminated before all animals have expressed estrus. This study was undertaken to compare the fit of three statistical distributions, the Weibull, the log-normal, and the linear hazard rate (LHR), to the empirical distribution of PPI for five treatment regimens: no bull exposure postpartum, bull exposure from 53 d postpartum, bull exposure from 3 d postpartum, and bull exposure from an average of 63 d postpartum for 2-yr-old cows and for mature cows. The Weibull and the log-normal distributions deviated considerably from the empirical distribution. The LHR distribution with parameters changing over three different regions gave an excellent fit. The resulting hazard rate (instantaneous probability of a cow expressing her first estrus at time t postpartum) revealed a low probability of expressing estrus within 27 d postpartum (43 d for 2-yr-olds). For cows not exposed to bulls, the hazard rate increased slowly with time. For cows exposed to bulls after 3 d postpartum, the hazard rate increased rapidly between d 27 and d 50. For cows exposed to bulls after 53 d postpartum, the hazard rate increased instantaneously approximately 12 d after initial exposure to bulls. This increase was also seen when cows were exposed to bulls beginning at a constant date (at an average of 63 d postpartum). Because of lack of fit, the Weibull and the log-normal distributions should not be used in survival analysis of PPI.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1977

Some quantitative results on Golgi impregnated axons in rat visual cortex using a computer assisted video digitizer.

Axonal fiber distributions of pyramidal cells in the visual cortex of the albino rat have been investigated using the rapid Golgi method and modern data collecting techniques. Three dimensional coordinate information was extracted from Golgi-impregnated axonal networks using a computer-assisted video digitizer. Computer programs used this data to generate various statistical distributions. In particular, angular distributions of the initial collateral segments and their endpoints were examined and found to reveal anisotropies. Inspection of the spatial distributions of the endpoints indicated a clustering at two distinct levels with respect to the pyramidal cell from which they originate. Dynamic graphic displays of the three dimensional data have been obtained and presented in the form of computer tracings of various orthogonal projections.

Animals↗

PubMed1990

The distribution of physical, chemical and conformational properties in signal and nascent peptides.

Signal peptides play a major role in an as-yet-undefined way in the translocation of proteins across membranes. The sequential arrangement of the chemical, physical and conformational properties of the signal and nascent amino acid sequences of the translocated proteins has been compiled and analysed in the present study. The sequence data of 126 signal peptides of length between 18 and 21 residues form the basis of this study. The statistical distribution of the following properties was studied hydrophobicity, Mr, bulkiness, chromatographic index and preference for adopting alpha-helical, beta-sheet and turn structures. The contribution of each property to the sequence arrangement was derived. A hydrophobic core sequence was found in all signal peptides investigated. The structural arrangement of the cleavage site was also clearly revealed by this study. Most of the physical properties of the individual sequences correlated (correlation coefficient approximately 0.4) very well with the average distribution. The preferred occupancy of amino acid residues in the signal and nascent sequences was also calculated and correlated with their property distribution. The periodic behaviour of the signal and nascent chains was revealed by calculating their hydrophobic moments for various repetitive conformations. A graphical analysis of average hydrophobic moments versus average hydrophobicity of peptides revealed the transmembrane characteristics of signal peptides and globular characteristics of the nascent peptides.

Amino Acid Sequence↗

PubMed1972

Statistical analysis of the bioassay of continuous carcinogens.

In an experiment consisting of the continuous constant application of various carcinogenic regimens to a pure strain of experimental animals for a long period, the cancer incidence rates so caused may be studied and compared by the fit of an appropriate class of statistical distributions. In this paper we show that a Weibull distribution in which the age-specific cancer incidence rate rises as a power of time since first risk is more appropriate than a lognormal distribution. If the Weibull family of distributions is used, more information can be extracted from the data, and differences of toxicity between various regimens will not bias the comparison of their carcinogenic forces.

Animals↗