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PubMed1990

Assessment of relationships between site-specific variables.

The assessment of relationships between site-specific variables has been a matter of controversy because of the claim that periodontal sites within individuals can be used as independent observations in statistical models. One problem with this approach is the unreliability of the calculated Type I and Type II error rates. Another problem is that such inappropriate analysis may prohibit a correct assessment of causal relationships between site-specific variables. The host-factor can act as an effect modifier and modulate the magnitude of the site-specific effects and/or the host-factor can act as a confounder by superimposing a patient-effect on the studied site-specific effects leading to bias. As a result, site-specific biological mechanisms of disease progression may be misinterpreted. Sites can be used as the experimental unit of analysis, but the sampling design from which the site-specific data originated should not be ignored.

Causality↗

PubMed2006

The potential prognostic value of some periodontal factors for tooth loss: a retrospective multilevel analysis on periodontal patients treated and maintained over 10 years.

BACKGROUND: The great challenge in clinical periodontology is assigning a prognosis to a periodontally affected patient. Many different factors can affect the long-term maintenance of periodontally compromised teeth. The main questions usually considered by the periodontist are: 1) Will a tooth lose more bone in the future? 2) Will the tooth itself be lost in the future? The purpose of this retrospective study was to evaluate the value of some clinical, genetic, and radiographic variables in predicting tooth loss in periodontal patients (aged 40 to 60 years) treated and maintained for 10 years. METHODS: Sixty consecutive non-smoking patients (aged 46.77 +/- 4.96 years) with moderate to severe chronic periodontitis (CP) were treated with scaling and root planing (SRP). Some patients also underwent additional surgical treatments. All patients were maintained in the same private practice for 10 years. The frequency of recall appointments was 3.4 +/- 1.0 months. At baseline (T(0)) and 10 years later (T(2)) the following clinical variables were evaluated: the number of teeth, probing depths (PD), tooth mobility (TM), and presence of prosthetic restorations (PR). In addition, radiographic measurements were taken of the mesial and distal distances from the cemento-enamel junction (CEJ) to the bottom of the defect (BD), to the bone crest (BC), and to the root apex (RA). At T(2), a genetic test to determine the IL-1 genotype and genetic susceptibility for severe periodontal disease was performed for all 60 patients, and they were classified as IL-1 genotype positive (G+) or negative (G-) according to the test results. Tooth loss was used as the outcome variable. Different predictor variables were then tested using a two-level statistical model (patient and tooth levels). At the patient level, these were: age, gender, mean bone loss (mean CEJ-BD)(T0), the interleukin-1 (IL-1) genotype, the interaction between mean bone loss, and IL-1 genotype (mean CEJ-BD(T0) x IL-1 genotype). At the tooth level, the variables were: TM(T0), prosthetic restorations (PR)(T0), molar teeth (MT)(T0), the infrabony component of the defect (BC-BD)(T0), PD(T0), bone level (CEJ-BD)(T0), and residual supporting bone (BD-RA)(T0). RESULTS: Among the considered predictor variables, the following were significantly associated with the outcome variable: 1) MT(T0) (P <0.0001); 2) BC-BD(T0) (P = 0.0377); and 3) BD-RA(T0) (P <0.0001). MT(T0) were found to be more prone to loss and the amount of BD-RA(T0) prognostic for tooth loss: the lower the residual amount of supporting bone, the higher the probability of tooth loss. Conversely, the BC-BD(T0)was associated with a reduced probability of future tooth loss: the greater the infrabony component, the lower the probability of tooth loss. None of the other considered predictors proved predictive for tooth loss. CONCLUSIONS: Within the scope of this study, many traditional prognostic factors were ineffective in predicting future tooth loss and, therefore, were of no prognostic value. Conversely, a few specific factors at the tooth level emerged as viable prognostic factors. The use of these factors may be of great value to practitioners as predictors of tooth loss when assigning a prognosis.

Adult↗

PubMedDate not supplied

Denitrification losses from outdoor piglet production: spatial and temporal variability.

Animal welfare considerations have stimulated the development of outdoor piglet (Sus scrofa) production systems, but the high levels of nutrients excreted suggest that nutrient losses from this system may be high. This study first described the spatial distribution of denitrification activity in a 5- x 5-m grid within and outside a paddock immediately after the sows (32 sows ha(-1) for 6 mo) were removed in October 1997, and again the following March. Denitrification rates averaged 0.01 kg N ha(-1) d(-1) outside, and 0.5 kg N ha(-1) d(-1) inside the paddock in October, while the corresponding figures in March were 0.01 and 0.1 kg N ha(-1) d(-1). The highest denitrification rates were observed around the feeder, and this was also the case for concentrations of dissolved organic C and inorganic N in the soil. A statistical model that included both soil parameters and distance to feeder and huts gave the best description of the variability, but there was no significant autocorrelation between sampling points. In a second phase, seasonal variation of denitrification activity within a paddock (12 sows ha(-1) yr(-1)) was quantified; 10 soil cores were sampled along a transect 11 times between March 1998 and February 1999. There was a significant positive effect of dissolved organic carbon (DOC) on denitrification at <25% gravimetric soil moisture (i.e., to November in this study). Both climate and management (position of huts and feeder) appeared to influence denitrification, which was estimated to be 69 kg N ha(-1) yr(-1), or 11% of the N surplus of this production system.

Animal Welfare↗

PubMed2002

Quantitative genetics of traits associated with hip dysplasia in a canine pedigree constructed by mating dysplastic Labrador Retrievers with unaffected Greyhounds.

OBJECTIVE: To determine the genetic influence on expression of traits associated with canine hip dysplasia. ANIMALS: 193 dogs from an experimental canine pedigree. PROCEDURE: An experimental canine pedigree was developed for linkage analysis of hip dysplasia by mating dysplastic Labrador Retrievers with nondysplastic Greyhounds. A statistical model was designed to test the effects of Labrador Retriever and Greyhound alleles on age at detection of femoral capital epiphyseal ossification, 8-month distraction index, and 8-month dorsolateral subluxation score. RESULTS: The additive effect was significant for age at detection of femoral capital epiphyseal ossification. Restricted maximum likelihood estimates (+/-SD) for this trait were 6.4+/-1.95, 10.2+/-2.0, 10.8+/-3.1, 11.4+/-2.1, and 13.6+/-4.6 days of age for Greyhounds, Greyhound backcross dogs, F1 dogs, Labrador Retriever backcross dogs, and Labrador Retrievers, respectively. The additive effect was also significant for the distraction index. Estimates for this trait were 0.21+/-0.07, 0.29+/-0.15, 0.44+/-0.12, 0.52+/-0.18, and 0.6+/-0.17 for the same groups, respectively. For the dorsolateral subluxation score, additive and dominance effects were significant. Estimates for this trait were 73.5+/-4.1, 71.3+/-6.5, 69.1+/-6.0, 50.6+/-12.9, and 48.4+/-7.7%, respectively, for the same groups. CONCLUSIONS: In this canine pedigree, traits associated with canine hip dysplasia are heritable. Phenotypic differences exist among founder dogs of each breed and their crosses. This pedigree should be useful for identification of quantitative trait loci underlying the dysplastic phenotype.

Animals↗

PubMed1992

Female traits, ovary and follicle characteristics, and the conditional probability of normal oocyte development after superovulation of beef cows.

The proportion of transferable beef embryos obtained after superovulation, follicle aspiration, and in vitro maturation and fertilization has been small. To seek possible explanations, cows on different planes of nutrition were treated with exogenous gonadotropin and oocytes were isolated from their ovaries. The record for each oocyte included characteristics of the follicle, ovary, and cow from which it was obtained and the response to in vitro maturation, fertilization, and development. The sample was used to obtain estimates of the relationships among the variables. The logistic function with the probability of normal development as the dependent variable was the basic equation of the statistical model. When an explanatory variable was itself a result of the biological system, an equation explaining variation therein was added to the model. Had equations representing endogenous regressors not been added to the model a simple, single equation would have represented oocyte development response; given an oocyte at aspiration only one variable, cumulus quantity, was found to condition the probability of normal development directly. However, the complete model included four additional equations: 1) the probability that an oocyte was recovered at aspiration was conditional on the plane of nutritional treatment and progesterone concentration in follicular fluid; 2) cumulus quantity was conditional on the presence on a corpus luteum, follicle size, and progesterone concentration; 3) progesterone concentration was dependent on plane of nutrition; and 4) corpus luteum was conditional on plane of nutrition. The estimated model provided some insight into the complexity of oocyte development response and the role nutrition may play.

Animal Nutritional Physiological Phenomena↗

PubMed1995

Factors affecting the developmental stage of embryos recovered on day 7 from superovulated dairy cattle.

The objective of this retrospective study was to evaluate the factors influencing developmental stage of bovine embryos recovered from superovulated dairy cattle 7 d after estrus. From 217 superovulated dairy cows and heifers, 2,211 eggs were recovered, of which 1,495 were classified as transferable embryos based on morphological evaluation of developmental stage and quality. From the evaluated embryos, 1,429 were non-surgically transferred to recipients to produce 623 calves. The transferable embryos were classified into five developmental stages and four quality grades. The least-developed transferable embryos tended to be classified into poorer quality grades. A multifactorial statistical model was used to analyze whether the following factors were associated with the developmental stage and quality grade of the embryos: donor breed, parity, gonadotropin preparation, embryo sex, insemination bull, embryologist (the person evaluating the embryo), year, and season of recovery. Among these factors, only the embryologist and the donor animal accounted for significant variation in embryo development. It was concluded that the developmental stage of embryos recovered at d 7 from superovulated cattle, when evaluated by simple morphological criteria, was correlated with the embryo's quality and was affected by the donor animal but in this study not by the embryo sex, donor breed and parity, gonadotropin preparation, and insemination bull used. The embryo's quality grading was influenced by the embryologist. Consequently, sexing of an embryo recovered from superovulated cattle is not possible by simple morphological evaluation of the embryo's developmental stage.

Animals↗

PubMed2002

Inbreeding effects on the parameters of the growth function in three strains of Iberian pigs.

The growth performance of inbred pigs coming from full-sib matings was compared to that of contemporary animals coming from the same sires mated to control dams. The animals belong to three strains of Iberian pigs with different histories of previous inbreeding. The data consisted of 1,615 weight records between 50 and 250 d of age from 229 pigs. The statistical model assumed the two parameters that describe the linear growth function (a = intercept, b = slope) as different traits (weight at 120 d and daily gain) and the analysis was carried out in a Bayesian framework via Gibbs sampling. The means of the posterior distribution of heritabilities, common litter environmental coefficients, and genetic correlation were 0.328 (h(2)a), 0.332 (h2b), 0.084 (c(2)a), 0.060 (c(2)b) and 0.973 (rhoG). Inbreeding depression, expressed as the performance decrease relative to the mean, per 10% increase of the inbreeding coefficient, was -3.18, -2.31 and -5.37% for weight at 120 d (a), and -3.16, -2.08 and -6.49% for daily gain (b) in each of the three strains. The results indicate that the inbreeding effects are dependent on the level of previous inbreeding, the more previous inbreeding, the less inbreeding depression.

Animals↗

PubMed2004

The DGAT1 K232A mutation is not solely responsible for the milk production quantitative trait locus on the bovine chromosome 14.

The gene, acyl-CoA:diacylglycerol acyltransferase1 (DGAT1), was recently identified as the one underlying the quantitative trait locus (QTL) for milk production traits in the centromeric region of the bovine chromosome 14. Until now, 2 alleles, the lysine variant (increasing fat yield, fat and protein percentage) and the alanine variant (increasing protein and milk yield), were postulated at DGAT1. This study investigated whether the diallelic DGAT1 polymorphism is responsible for all the genetic variation at the centromeric region of this chromosome for milk, fat, and protein yield and fat and protein percentage. A statistical model was applied to a granddaughter design to analyze 16 German Holstein families. The model included the diallelic DGAT1 effect and the QTL transition probability estimated for each chromosomal position by a multiple marker approach. Because the regression coefficient of this probability was corrected for the diallelic DGAT1 polymorphism, it represented a putative conditional QTL effect. The effect of the DGAT1 gene was always highly significant. The conditional QTL effect was significant genomewise for fat percentage at the proximal end of the chromosome and for protein percentage at a more distal chromosomal region. Additional chromosomewise significance was found for fat and protein yield. Our results suggest an additional source of genetic variance on this chromosome for these traits; either one or more additional alleles segregating at DGAT1 that were not previously detected, a second quantitative trait locus affecting these traits, or both.

Acyltransferases↗

PubMed2006

Estimating receiver operating characteristic curves with covariates when there is no perfect reference test for diagnosis of Johne's disease.

Paratuberculosis (Johne's disease) is a significant animal health problem. Evaluation of diagnostic tests for Johne's disease has been difficult due to lack of a gold standard test. In recent years, there has been interest in receiver operating characteristic (ROC) curve estimation without any gold standard test. Typically, either Bayesian or maximum likelihood methods are proposed. Although these methods overcome the lack of a gold standard test in ROC curve estimation, little work has been done to incorporate covariates in the analysis. In this paper, we propose a method for estimation of ROC curves based on statistical models to adjust for covariate effects when the true disease states of test animals are unknown. The covariates may be correlated with the disease process or with the diagnostic testing procedure, or both. We propose a 2-part Bayesian model: first, a logistic regression model for disease prevalence is used to fit the covariates; second, a linear model is used to fit the covariates to the distribution of test scores. We used Markov chain Monte Carlo methods to compute the posterior estimates of the sensitivities and specificities that provide the groundwork for inference concerning the diagnostic procedure's accuracy. We applied the methodology to milk ELISA scores from several dairy-cow herds for the diagnostic testing of paratuberculosis. We found that both milk yield and its interaction with age had significant effects on the disease process whereas only milk yield was significant on the testing procedure.

Animals↗

PubMed1990

Milk production and somatic cell count in Michigan dairy herds.

The established association between milk production and SCC in dairy cattle is increasingly used to estimate lost production due to mastitis. Such cost estimates are used to make decisions regarding cost effective mastitis prevention and control. It is therefore important to verify the relationship between SCC and milk production using data from different areas of the country and by using different analytical methodology. Our study used the 1985 to 1986 Michigan DHIA data base and analyzed daily milk production records rather than lactation summary records as used in the past. One advantage to our approach was that it did not give equal weight to all lactations, regardless of their duration. Also, it enabled inclusion of cows that had incomplete lactations caused by culling, or had other reasons for removal from the herd. A statistical model was constructed to predict milk production on the basis of herd, cow within herd, stage in lactation, month of calving, lactation, and SCC. The data base contained 397,172 milk test records obtained from Michigan DHIA from 504 Holstein herds in Michigan's lower peninsula. Our final model predicted 78% of the variation in milk production. Prediction of milk loss for each herd was highly correlated (r = .98) with the prediction model adopted by most DHIA organizations. Our model predicted that the mean herd lost a mean of 1.17 kg of milk/cow per d associated with SCC.

Age Factors↗

PubMed1995

Age and seasonal effects on Holstein yield for four regions of the United States over time.

Multiplicative factors to adjust Holstein yield for age and season of calving were calculated and analyzed from 20 data files for region and time. Regions were 1) California, 2) Minnesota and Wisconsin, 3) New York and Pennsylvania, and 4) six southern states (Texas, Louisiana, Mississippi, Alabama, Georgia, and Florida). Time periods were calving years of 1964 to 1968, 1971 to 1975, 1976 to 1980, 1981 to 1985, and 1986 to 1990. The same statistical model was used that had been used to derive current USDA factors from 1964 to 1968 data. The number of lactation records for each data file ranged from 81,394 to 2,238,201 and increased with time. Effect of calving season on milk yield generally decreased with time; the largest decrease was for the southern region. Effect of calving age also generally decreased for recent data, and the largest decreases were for California. Updated factors to adjust yield for calving age and season are indicated for some regions.

Aging↗

PubMed2006

The effect of psychoemotional load on ventricular repolarization reflected in integral body surface potential maps.

The aim of the present study was to investigate the reflection of psychoemotional stress in the body surface potential distribution as documented by isointegral maps of cardiac activation and recovery. In 72 young men (18.3+/- 7.3 y.) with no cardiovascular history body surface potential maps (BSPMs) at rest and during the test of mental arithmetic were recorded. The digitalized data for each point of the QRS, STT and QRST integral maps, for each subject in both situations, were processed and evaluated by methods of univariate as well as spatial mathematical and statistical modeling. The results showed during MA a significant decrease of repolarization integral values over the sternum and right precordium, which contributed to analogically localized decrements also in the QRST BSM. The decrease occurred in more than 2/3 of lead points. The most pronounced changes were observed in the right precordial area, where potentials decreased in more than in 70 % of subjects. In conclusion, the discriminative power of the difference STT and QRST integral maps was strong enough to distinguish the mental arithmetic induced changes in the superficial cardiac electric field. These adrenergic transient alterations in ventricular recovery may be of importance in subjects at risk for ventricular arrhythmias.

Body Surface Potential Mapping↗

PubMed1991

A retrospective analysis on the epizootiological aspects of outbreaks of Pasteurella anatipestifer infection in turkeys in Minnesota.

The possible risk factors associated with outbreaks of Pasteurella anatipestifer infection in turkeys were analyzed to study the epizootiology of the disease. The data for the study was obtained from flocks affected and unaffected with Pasteurella infection. The results of the analysis suggested that overcrowding, preexisting viral infections, increased activity of wild birds on the farm, and shorter down time were possible factors that initiate the occurrence of the disease in turkey flocks. The statistical models used in the analysis predicted correctly 80% of the unaffected flocks (8 out of 10 flocks), and 95% of the affected flocks (13 out of 14 flocks). The overall correct prediction was 88% (21 out of 24 flocks). Fish meal and meat and bone meal, which are integral components of turkey feed, were analyzed for the possible presence of P. anatipestifer. Its presence in a sample of fish meal was demonstrated.

Animal Feed↗

PubMed2004

Relationship between costs and symptoms in schizophrenia patients treated with antipsychotic medication: a review.

BACKGROUND: The purpose of this review is to understand how changes in costs of illness are related to the effects of antipsychotic medications on symptoms in schizophrenia patients. METHOD: A search of the MEDLINE database was performed using the keywords costs, symptoms, and schizophrenia. Studies published between 1965 and 2003 in English, French, German, or Spanish that assessed costs, symptoms, and relationships between costs and symptoms were reviewed. RESULTS: Twenty studies were identified. Most of the reviewed clinical trials of antipsychotic medications reported a decrease in mean costs of illness and an improvement in symptoms. However, many of the studies did not examine the relationship between changes in costs and symptoms. CONCLUSION: There is little evidence that changes in costs of illness are directly related to the effects of antipsychotic medications on symptoms. This review emphasizes the need for standardizing the assessment of costs and clinical outcomes, looking more specifically at the relationship between types of costs and specific aspects of psychopathology and developing new statistical models relating changes in costs and clinical outcomes.

Antipsychotic Agents↗

PubMed2006

Relationships between host infectivity to mosquitoes and asexual parasite density in Plasmodium falciparum.

We describe a statistical model for the relationship between asexual parasite densities of Plasmodium falciparum and the infectivity of the host to mosquitoes. The model takes into account the delay between asexual parasitemia and infectivity resulting from the time course of gametocytemia. It also allows for the need for the blood meal to contain gametocytes of both sexes if infection is to take place. We show that by fitting this model to data from malariatherapy patients it can explain observed patterns of infectiousness of the human host and is consistent with distributions of gametocyte densities in malariatherapy patients. By integrating this model into an individual-based simulation of human populations exposed to endemic P. falciparum transmission, we are able to predict the contributions of different host age groups to the infectious reservoir. Comparison of model predictions with published estimates of this quantity confirms that infected adults hosts are likely to make a significant contribution to the reservoir of transmission, and points to the need for improved population-based estimates of this age-dependence in infectivity of humans in endemic areas.

Animals↗

PubMed2001

A novel approach for evaluating level, frequency and duration of lumbar posture simultaneously during work.

OBJECTIVES: Electrogoniometers are used to collect continuous information on postural distributions among workers. Enormous quantities of data are generated that have to be reduced to meaningful parameters (angle, frequency, and duration). In this study we propose statistical models to determine these essential characteristics of postural load on nurses, housekeepers, and office workers. METHODS: A direct registration of the lumbar posture was made over a workday with an inclinometer. An exposure variation analysis was used to summarize information on the angle of trunk flexion, the time period of maintained postures, and the percentage of worktime in a data matrix. A hierarchical regression analysis was used to compare these characteristics among nurses (N=64), housekeepers (N=16), and office workers (N=27). RESULTS: The occupational groups did not differ for either frequency or duration of trunk flexion over 30 degrees since frequency and duration were inversely related. Nurses experienced longer worktimes than the office workers did for trunk flexion between 30 and 70 degrees maintained <5 seconds, whereas office workers experienced longer worktimes in smaller angles (< 30 degrees) for longer periods. Comparable differences in the distributions of postural load were found between housekeepers and office workers. CONCLUSIONS: This study describes the use of hierarchical models in analyses of the exposure level, frequency, and duration of postural load simultaneously and offers an alternative to conventional ergonomic analysis in which the dynamics of exposure are often ignored. The distinction in postural load between nurses or housekeepers and office workers is best determined by the combination of trunk angle and time period.

Biomechanical Phenomena↗

PubMed1997

Improving the statistical approach to health care provider profiling.

This paper reviews and compares existing statistical methods for profiling health care providers. It recommends improvements that are based on the use of better statistical models and the adoption of more realistic, medically based criteria for judging the performance of health care providers. Unlike most profiling methods, the proposed hierarchical models allow the probability of acceptable provider performance to be calculated; thus, they can answer such questions as, "What is the probability that a given hospital's true mortality rate for cardiac surgery patients exceeded 3.33% last year?" The commonly encountered problems of regression-to-the-mean bias and small caseloads can be handled by using hierarchical models to extract more information from profiling data.

Bayes Theorem↗

PubMed1998

[The number of beds needed for patients with infectious diseases that require hospitalization by law].

PURPOSE: Using a statistical model, a study was conducted on the number of beds that are needed for patients with infectious diseases who are required by law to be hospitalized. METHODS: Based on 1995 data, the incidence of such infectious diseases and the average duration of isolation of these patients in Japan were obtained. Using a Poisson distribution, the probability that the number of patients that exceeds a specific number over an average duration of hospitalization was computed in a finite population. The observation period was then extended to one year and the probability that the number of patients did not exceed a specific number during one year was calculated. RESULTS: In 1995, the annual incidence of infectious diseases requiring isolation by hospitalization was 1.38 per 100,000 population and the average duration of hospital confinement was 13.8 days. The estimated patient numbers calculated based on the probability of less than 0.001 that the number of patients would not exceed a specific number were: 2 for 30,000 population, 3 for 50,000 through 100,000, 5 for 200,000 and 300,000, 5 for 400,000 and 500,000, 6 for 750,000 and 1,000,000, 8 for 2,000,000, and 10 for 3,000,000. CONCLUSION: By using a Poisson distribution, a method was developed for estimating the number of beds that are needed for patients with infectious diseases when hospitalization was mandatory.

Communicable Disease Control↗