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At least 883 records · Page 49Linked to original sources
PubMed2003

Estimates of breed average direct, maternal and heterosis effects for some pre-weaning traits of Zebu breeds and their crosses in southeastern Mexico.

Information on 936 birth weights (BW), adjusted weaning weights (AWW) and average daily gains (ADG) from Brahman (B), Indubrazil (I), Gyr (G) and commercial Zebu (C) cattle and their crosses were obtained from the records of a farm in the State of Yucatan, Mexico. Two statistical models were used to analyse the data: the first included the effects of year and season of birth, sex of the calf, cow's parity number and breed group. The other model included the same environmental effects as the previous model and the genetic components of breed group (breed additive, breed maternal and heterosis effects). Additive and maternal effects were expressed as deviations from those for the B breed. The means of BW. AWW and ADG for the B breed were 33.3 +/- 0.64 kg, 204.0 +/- 4.9 kg and 760.06 +/- 19.24 g/day, respectively. Both models gave similar results in terms of the variance explained. Additive effects were significant (p < 0.05) for AWW and ADG but not for BW. The minor additive effect was for the C breed (-10.75 kg and 40.77 g for WW and ADG, respectively). Maternal and heterosis effects were not significant (p > 0.05) for any of the traits. The correlation between the breed group means and the means estimated by the prediction equation was r = 0.88. Finally, there was no significant genetic effect on pre-weaning calf performance among the genotypes evaluated. The genetic model can be used to predict the genotype means with a high degree of accuracy.

Animals↗
PubMed2000

Vitamin C concentrations in plasma as a function of intake: a meta-analysis.

The purpose of this study was to estimate the intake-plasma relationship for vitamin C by means of a meta-analysis. A MEDLINE search revealed 30 publications matching our inclusion criteria. We completed the set with 5 older papers and with one monograph. The proposed statistical model corrects for inconsistencies with regard to methodological differences between the various studies. Therefore, the contribution of a particular study to the estimation is independent of the number of data points. The estimations were performed for the complete data set as well as for different subgroups: "adult" aged 15-65 years, "elderly" aged 60-96 years, "nonsmokers" and "smokers". The 50th percentile of the plasma concentration for a daily vitamin C intake of 60 mg was 42.4 mumol/L. The corresponding values for the different subgroups were: "adult" 44.1 mumol/L, "elderly" 31.0 mumol/L, "nonsmokers" 42.4 mumol/L, and "smokers" 33.6 mumol/L. Thus, this meta-analysis confirms earlier results that the requirements of vitamin C is higher in "elderly" and "smokers" compared to "adult" and "nonsmokers" and it can be used for the estimation of the vitamin C intake in order to achieve a desired plasma level within a target population. In the general population the assumed optimal plasma concentration of 50 mumol/L, as proposed by a consensus conference, can be achieved by the intake of 100 mg per day, which is the new recommendation of the Austrian, German, and Swiss Nutrition Societies.

Adolescent↗
PubMed2003

Haemoglobin during pregnancy: relationship to erythropoietin and haematinic status.

OBJECTIVE: To investigate the effect of haematinic status on erythropoietin throughout pregnancy in order to assess whether haematinic supplementation is appropriate for all pregnant women or should be reserved for individuals in whom deficiency has been identified. METHODS: A prospective, repeated-measures, longitudinal study of 263 women enrolled at an antenatal clinic in a district general hospital who received standard obstetric management including haematinic supplements. Haematological indices, iron status, folate and B12 status, and erythropoietin levels were measured by standard methods at scheduled intervals throughout pregnancy. The relationships between the measurements were analysed using statistical models which took into account the serial correlation between repeated measurements on the same individuals. RESULTS: Erythropoietin levels rose throughout pregnancy from a mean of 22.8 mU/mL at booking to 43.7 mU/mL at 38 wk. There was a significant relationship between erythropoietin levels and haemoglobin, ferritin, TIBC and folate. The relationship was strongest between erythropoietin and haemoglobin. Erythropoietin levels were influenced by parity but not maternal age. CONCLUSION: Haematinic levels, particularly iron are related to the rise in serum EPO which occurs during pregnancy. Therefore, haematinic deficiency in pregnancy will result in increased stimulation of erythroid progenitor cells by erythropoietin. While haematinic supplementation is not always prescribed throughout pregnancy, haematinic status must be assessed on an individual basis and supplementation provided as required.

Adult↗
PubMed2001

Airborne birch and grass pollen allergens in street-level shops.

Polluted urban outdoor air may be enriched with large amounts of submicronic respirable pollen allergen particles that penetrate into street-level shops. The objectives of the study were to map concentrations of birch and grass pollen allergens in indoor air of street-level shops and to explore the effect of electrostatic air cleaning under authentic working conditions, indoor air samples were collected in May and July 1999 in two shops. Allergens were quantified by a direct on sampling filter in solution (DOSIS) luminescence immunoassay. The average concentration of airborne indoor birch pollen allergen in the shop with air cleaning was estimated to be 20 +/- 9 SQ/m3 (mean +/- SD) compared to 31 +/- 17 SQ/m3 (mean +/- SD) of that without. The air cleaner reduced the indoor air birch pollen allergen concentration by on average 26 to 48% (P < 0.05). Corresponding figures for airborne indoor grass pollen allergen concentrations were 14 +/- 7 SQ/m3 and 17 +/- 8 SQ/m3, indicating a statistically non-significant (t-test) average 18% reduction of allergen by air cleaning. Excluding two observations with poor fit to the statistical model a significant (P < 0.05) average 27% reduction was obtained. Substantial amounts of airborne birch and grass pollen allergens may occur in street-level shops during flowering seasons.

Air Pollutants↗
PubMed1999

Recovery after treatment and sensitivity to base rate.

Accurate classification of patients as having recovered after psychotherapy depends largely on the base rate of such recovery. This article presents methods for classifying participants as recovered after therapy. The approach described here considers base rate in the statistical model. These methods can be applied to psychotherapy outcome data for 2 purposes: (a) to determine the robustness of a data set to differing base-rate assumptions and (b) to formulate an appropriate cutoff that is beyond the range of cases that are not robust to plausible base-rate assumptions. Discussion addresses a fundamental premise underlying the study of recovery after psychotherapy.

Bayes Theorem↗
PubMed2000

Permanency and ephemerality of psychological measures with application to organizational commitment.

The constancy or change of an attribute is important to most substantive areas of psychology. During the past decade, 2 independent methodological schools have developed statistical models for the depiction of longitudinal research. One, which might be called the European school, has created latent state-trait models. Alternatively, the American school has formulated models that go by the rubric of latent curve analysis or latent growth models. In this article, the authors integrate both approaches into a detailed unified latent curve and latent state-trait model (LC-LSTM) that includes the significant features from both schools. From the LC-LSTM framework, the permanency and ephemerality of psychological measures are discussed and the concepts of stability and reliability are reformulated. In addition, a comprehensive illustration on organization commitment is presented.

Humans↗
PubMed2001

Informatics and multiplexing of intact protein identification in bacteria and the archaea.

Although direct fragmentation of protein ions in a mass spectrometer is far more efficient than exhaustive mapping of 1-3 kDa peptides for complete characterization of primary structures predicted from sequenced genomes, the development of this approach is still in its infancy. Here we describe a statistical model (good to within approximately 5%) that shows that the database search specificity of this method requires only three of four fragment ions to match (at +/-0.1 Da) for a 99.8% probability of being correct in a database of 5,000 protein forms. Software developed for automated processing of protein ion fragmentation data and for probability-based retrieval of whole proteins is illustrated by identification of 18 archaeal and bacterial proteins with simultaneous mass-spectrometric (MS) mapping of their entire primary structures. Dissociation of two or three proteins at once for such identifications in parallel is also demonstrated, along with retention and exact localization of a phosphorylated serine residue through the fragmentation process. These conceptual and technical advances should assist future processing of whole proteins in a higher throughput format for more robust detection of co- and post-translational modifications.

Algorithms↗
PubMed1999

Quantifying the effect of population mixing on childhood leukaemia risk: the Seascale cluster.

A statistical model was developed based on Poisson regression of incidence of childhood leukaemia and non-Hodgkin's lymphoma (NHL) in relation to population mixing among all 119 539 children born 1969-1989 to mothers living in Cumbria, north-west England, (excluding Seascale). This model was used to predict the number of cases in Seascale (the village adjacent to the Sellafield nuclear installation) children, born 1950-1989 and diagnosed before 1993. After allowing for age, the incidence of acute lymphoblastic leukaemia (ALL) and NHL was significantly higher among children born in areas with the highest levels of population mixing, relative risk (RR) = 11.7 (95% confidence interval (CI) 3.2-43) and was highest among children of incomers. The model predicted up to 3.0 (95% CI 1.3-6.0) cases of ALL/NHL in children born in Seascale compared to six observed and 2.0 (95% CI 1.0-3.4) cases in children resident, but not born, in Seascale compared to two observed. Population mixing is a significant risk factor for ALL/NHL, especially in young children, accounting for over 50% of cases in Cumbria and most cases in Seascale.

Adolescent↗
PubMed2005

Effects of ultrafine and fine particulate and gaseous air pollution on cardiac autonomic control in subjects with coronary artery disease: the ULTRA study.

Previous studies have shown an association between elevated concentrations of particulate air pollution and cardiovascular morbidity and mortality. Therefore, the association between daily variation of ultrafine and fine particulate air pollution and cardiac autonomic control measured as heart rate variability (HRV) was studied in a large multicenter study in Amsterdam, the Netherlands, Erfurt, Germany, and Helsinki, Finland. Elderly subjects (n=37 in Amsterdam, n=47 in both Erfurt and Helsinki) with stable coronary artery disease were followed for 6 months with biweekly clinical visits. During the visits, ambulatory electrocardiogram was recorded during a standardized protocol including a 5-min period of paced breathing. Time and frequency domain analyses of HRV were performed. A statistical model was built for each center separately. The mean 24-h particle number concentration (NC) (1,000/cm(3)) of ultrafine particles (diameter 0.01-0.1 microm) was 17.3 in Amsterdam, 21.1 in Erfurt, and 17.0 in Helsinki. The corresponding values for PM2.5 were 20.0, 23.1, and 12.7 microg/m(3). During paced breathing, ultrafine particles, NO(2), and CO were at lags of 0-2 days consistently and significantly associated with decreased low-to-high frequency ratio (LF/HF), a measure of sympathovagal balance. In a pooled analysis across the centers, LF/HF decreased by 13.5% (95% confidence interval: -20.1%, -7.0%) for each 10,000/cm(3) increase in the NC of ultrafine particles (2-day lag). PM2.5 was associated with reduced HF and increased LF/HF in Helsinki, whereas the opposite was true in Erfurt, and in Amsterdam, there were no clear associations between PM2.5 and HRV. The results suggest that the cardiovascular effects of ambient ultrafine and PM2.5 can differ from each other and that their effect may be modified by the characteristics of the exposed subjects and the sources of PM2.5.

Aged↗
PubMed2006

Guidelines for statistical analysis of percentage of syllables stuttered data.

PURPOSE: The purpose of this study was to develop guidelines for the statistical analysis of percentage of syllables stuttered (%SS) data in stuttering research. METHOD: Data on %SS from various independent sources were used to develop a statistical model to describe this type of data. On the basis of this model, %SS data were simulated with varying means, standard deviations, and sample sizes. Four methods for analyzing %SS were compared. RESULTS: Results suggested that %SS data can be adequately modeled with a gamma distribution. Simulations based on a gamma distribution showed that all 4 analysis techniques performed favorably with respect to Type I error except for F. E. Satterthwaite's (1946) t test, which had increased Type I error on two occasions. Power was generally lower for the Wilcoxon-Mann-Whitney test compared with the other methods. Analysis of variance (ANOVA) performed on square-root-transformed data performed adequately under all scenarios, but ANOVA performed on nontransformed data and Satterthwaite's t test performed poorly when sample sizes were small or when sample sizes and variances of the groups were markedly different. CONCLUSIONS: Standard techniques such as t test and ANOVA are appropriate for most analysis scenarios with %SS data. Two occasions when this is not the case are when sample size is small, with fewer than 20 in each group, or when sample sizes and variances of the groups are markedly different. Under these circumstances, analyses should be based on standard methods, with a suitable transformation performed prior to analysis.

Analysis of Variance↗
PubMed2001

Ambient temperature effects on the extrinsic incubation period of Wuchereria bancrofti in Aedes polynesiensis: implications for filariasis transmission dynamics and distribution in French Polynesia.

Temperature effects on development of the human filarial parasite Wuchereria bancrofti (Cobbold) (Filaridea: Onchocercidae) in the main Pacific vector Aedes polynesiensis Marks (Diptera: Culicidae) are analysed in relation to ambient climatic conditions. A statistical model of the extrinsic cycle duration as a function of temperature is described and used to distinguish three patterns of W. bancrofti transmission dynamics: continuous, fluctuating and discontinuous, occurring from north to south geographically among French Polynesian archipelagos. In the northerly Marquesas Islands (8-11 degrees S) filariasis transmission is continuous and very active, facilitated by perennially high temperatures combined with constantly high rates of man-vector contact. In the southerly Australes Islands (21-28 degrees S) filariasis transmission is seasonally discontinuous and, during the cooler months (May-September), the model predicts virtually no transmission because the cycle duration exceeds the life expectancy of the vector. In the Society Islands (16-18 degrees S), between the Marquesas and Australes, transmission is predicted to be intermediate as expected from their latitude, with seasonally fluctuating transmission potential. In the Tuamotu Islands (also geographically intermediate: 14-23 degrees S), with theoretically perennial transmission potential, transmission occurs only intermittently, being limited by other human and environmental factors whereby man-vector contact is confined to seasonal agricultural situations. Generally, among French Polynesian archipelagos where Aedes polynesiensis is the vector, the transmission potential for W. bancrofti and resulting disease manifestations of lymphatic filariasis in humans are correlated with ambient temperature due to the degree of southern latitude.

Aedes↗
PubMed2003

Identification of stimulatory and inhibitory inputs to the hypothalamic-pituitary-adrenal axis during hypoglycaemia or transport in ewes.

This study used the novel approach of statistical modelling to investigate the control of hypothalamic-pituitary-adrenal (HPA) axis and quantify temporal relationships between hormones. Two experimental paradigms were chosen, insulin-induced hypoglycaemia and 2 h transport, to assess differences in control between noncognitive and cognitive stimuli. Vasopressin and corticotropin-releasing hormone (CRH) were measured in hypophysial portal plasma, and adrenocorticotropin hormone (ACTH) and cortisol in jugular plasma of conscious sheep, and deconvolution analysis was used to calculate secretory rates, before modelling. During hypoglycaemia, the relationship between plasma glucose and vasopressin or CRH was best described by log10 transforming variables (i.e. a positive power-curve relationship). A negative-feedback relationship with log10 cortisol concentration 2 h previously was detected. Analysis of the "transport" stimulus suggested that the strength of the perceived stimulus decreased over time after accounting for cortisol facilitation and negative-feedback. The time course of vasopressin and CRH responses to each stimulus were different However, at the pituitary level, the data suggested that log10 ACTH secretion rate was related to log10 vasopressin and CRH concentrations with very similar regression coefficients and an identical ratio of actions (2.3 : 1) for both stimuli. Similar magnitude negative-feedback effects of log10 cortisol at -110 min (hypoglycaemia) or -40 min (transport) were detected, and both models contained a stimulatory relationship with cortisol at 0 min (facilitation). At adrenal gland level, cortisol secretory rates were related to simultaneously measured untransformed ACTH concentration but the regression coefficient for the hypoglycaemia model was 2.5-fold greater than for transport. No individual sustained maximum cortisol secretion for longer than 20 min during hypoglycaemia and 40 min during transport. These unique models demonstrate that corticosteroid negative-feedback is a significant control mechanism at both the pituitary and hypothalamus. The amplitude of HPA response may be related to stimulus intensity and corticosteroid negative-feedback, while duration depended on feedback alone.

Adrenal Cortex Hormones↗
PubMed2002

Prediction of renal insufficiency in Pima Indians with nephropathy of type 2 diabetes mellitus.

BACKGROUND: A high prevalence and early onset of type 2 diabetes in Pima Indians is well known. Our objective is to use several statistical models to identify predictors of glomerular filtration rate (GFR) deterioration and develop an algorithm to predict GFR 4 years after the initial evaluation. METHODS: All records (n = 86) were randomly assigned to a training set (n = 60) and a testing set (n = 26). Linear regression, generalized additive, tree-based, and artificial neural network models were used to identify predictors of outcome and develop a prediction algorithm. RESULTS: Proteinuria remained the single most important predictor of long-term renal function; other predictors included baseline GFR, blood pressure, plasma renin activity, lipid profile, age, weight/body mass index, and diabetes duration. All four models achieved a good correlation (r = 0.73 to 0.78) between observed and predicted 4-year GFRs on a separate (testing) data set. Best results in predicting the value of GFR were achieved using a tree-based model with six terminal nodes (r = 0.78; root mean squared prediction error = 38.9). The tree-based and generalized additive models achieved high positive (91%) and negative (100%) predictive values in identifying subjects, who developed depressed GFRs in 4 years. An artificial neural network achieved the highest area under the receiver operating characteristic curve (0.91). CONCLUSION: GFR depression within 4 years can be predicted with a precision that suggests potential clinical utility. A tree-based model with six terminal nodes has shown the best results in predicting the actual value of GFR, whereas an artificial neural network is the model of choice to identify the group of patients that will develop renal insufficiency.

Adult↗
PubMed2000

Are we still performing inappropriate carotid endarterectomy?

OBJECTIVES: the 1998 ECST final report suggests that the decision to operate on patients with greater than 70% symptomatic stenosis should be based on a statistical model incorporating age, sex and degree of stenosis. The aim of this study was to identify patients operated on the basis of the 1991 reports who would not now be offered surgery according to the 1998 ECST recommendations and to determine the surgical morbidity and mortality arising from these <<< >>> CEAs. METHODS: interrogation of a prospectively gathered database of all CEAs performed for symptomatic stenosis between 1st January 1994 and 1st May 1998. CEAs were classified as <<< >>>, <<< >>> or <<< >>> according to the 1998 ECST recommendations. RESULTS: there were 154 males and 72 females (median age (range) was 67 (39-85) and 65 (38-81), respectively). In males 101 (66%) of CEAs were <<< >>>, 51 (33%) were <<< >>> and only two (1%) were <<< >>>. In women, the corresponding proportions were 13 (18%), 45 (63%) and 14 (19%), respectively. The combined peri-operative major stroke (Rankin 3-5) and death rate was 1.8% (4 patients). Of these, three, one and zero patients were in the <<< >>>, <<< >>> and <<< >>> groups. CONCLUSIONS: strict adherence to the 1998 ECST recommendations would reduce by 50% the number of CEAs currently performed in this vascular unit and, in general, would restrict CEA to a higher risk group. The validity of the ECST model requires further evaluation.

Adult↗
PubMed2001

Hepatitis C virus infection and needle exchange use among young injection drug users in San Francisco.

Young injection drug users (IDUs) in San Francisco may be at high risk for hepatitis C virus (HCV) infection despite access to several needle exchange venues. The authors conducted a cross-sectional study from 1997 to 1999 in San Francisco to estimate the prevalence and incidence of antibody to HCV (anti-HCV) among street-recruited IDUs under age 30, and to examine risk behaviors and sources of sterile needles. Among 308 participants, the prevalence of anti-HCV was 45%. Using statistical modeling, incidence of HCV infection was estimated to be 11 per 100 person years. Independent risk factors for anti-HCV included age (odds ratio [OR], 1.17 per year; 95% confidence interval [CI], 1.05-1.30), years injecting (OR, 1.21 per year; 95% CI, 1.10-1.34), years in San Francisco (OR, 1.06 per year; 95% CI, 1.00-1.14), first injected by a sex partner (OR, 4.06; 95% CI, 1.74-9.52), injected daily (OR, 3.85; 95% CI, 2.07-7.17), ever borrowed a needle (OR, 2.56; 95% CI, 1.18-5.53), bleached last time a needle was borrowed (OR, 0.50; 95% CI, 0.24-1.02), snorted or smoked drugs in the prior year (OR, 0.48; 95% CI, 0.26-0.89), and injected by someone else in the prior month (OR, 0.50; 95% CI, 0.25-0.99). In the prior month, 88% used at least 1 of several needle exchange venues, and 32% borrowed a needle. We conclude that anti-HCV prevalence is lower than in previous studies of older IDUs, but 11% incidence implies high risk of HCV infection in a long injecting career. Despite access to sterile needles, borrowing of needles persisted.

Adolescent↗
PubMed1997

Survival algorithms and outcome analysis in primary biliary cirrhosis.

The natural history of primary biliary cirrhosis (PBC) is one of slowly progressive cholestasis with liver damage, development of cirrhosis with its concomitant complications, and death unless the patient undergoes liver transplantation. Natural history studies have identified several variables associated with a decreased survival in patients with PBC. The course of the disease can be divided into three time periods: (1) a presymptomatic phase, probably lasting up to 20 years; (2) a symptomatic phase, with anicteric or mild jaundice, lasting up to 5 to 10 years; and (3) a preterminal or accelerated phase with marked jaundice, lasting up to 2 years. Since the course of the disease is one of slow progression leading to liver failure and death unless liver transplantation intervenes, several investigators have developed statistical models to predict survival. The ability to predict survival for individual patients with PBC has been valuable in the management of these patients, particularly in patient selection and timing of liver transplantation. In addition, survival estimates can be utilized in education and counseling patients and their families. These models may also be used to evaluate the efficacy of new treatments by comparing natural history survival with the survival achieved by therapeutic effect. Over the past several decades, the natural history models of PBC have been developed in the absence of effective medical therapy. The efficacy of liver transplantation and survival following liver transplantation has now been quantitatively established. Future efforts should be aimed at determining not only survival of patients with primary biliary cirrhosis in the presence of effective medical therapy but also at assessing the quality of life and cost-effectiveness of medical therapy and liver transplantation in the management of patients with primary PBC.

Algorithms↗
PubMed2004

Photophysics of protoporphyrin ions in vacuo: triplet-state lifetimes and quantum yields.

Lifetimes of triplet-state molecules and triplet quantum yields are important parameters in photobiology as they determine the generation of singlet-oxygen upon irradiation with visible light. Here we report lifetimes of protoporphyrin IX (pp) in vacuo measured in an ion storage ring. We find that after 532 nm photon absorption, pp(-) (free base and negatively charged carboxylate) and pp(+) (single protonation of ring nitrogen) have triplet-state lifetimes of 12 and 6 ms, respectively. After 415 or 390 nm absorption the lifetime of the anion is shorter (1.5 and 0.6 ms) as expected from the increase in temperature. Triplet quantum yields of pp(-) and pp(+) are similar, 0.6-0.7, close to values reported for the free base and monocation in solution. The other channel, direct decay to the electronic ground state and subsequent dissociation of vibrationally excited ions, is much faster than triplet-singlet intersystem crossing. We measured lifetimes of 63 micros, 96 micros, and 0.3 ms after 390, 415, and 532 nm excitation, respectively. A fit of a statistical model to the pp(-) decay results in an Arrhenius activation energy of 0.5+/-0.2 eV for CO(2) loss and a low preexponential factor (10(6)-10(10) s(-1)), indicative of an entropic barrier.

Absorption↗