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PubMedDate not supplied

Starch-encapsulated chlorpyrifos: release rate, insecticidal activity and degradation in soil.

Incorporation of chlorpyrifos into starch matrices was achieved by thermal gelatinization. The level of amylose content in the starch matrices (10 and 52%) and the addition of auxiliary agents, i.e. solvent, emulsifiers or both, were varied and eight different formulations were prepared. According to differential scanning calorimetry (DSC) and X-ray diffraction measurements, chlorpyrifos was partly present in a crystalline form in all the starch formulations. The formulations had controlled release properties, and the release rate into water could be described by a linear model. In a bioassay, the formulations killed all larvae of the cabbage root fly at a dosing of 1.4 kg a.i. per ha. The degradation of chlorpyrifos in soil from the starch formulations could be described in a non-linear logistic model and the half-life was predicted to be 88 days. Differences in the amount of amylose in the starch as well as the addition of solvent and emulsifiers in the preparation procedure had no systematic influence on the release rate, the insecticidal effect and the degradation rate. No correlation between release rate into water and degradation in soil could be established. Two commercial chlorpyrifos formulations Lorsban 15 G (granular) and Cyfos 500 gl(-1) (emulsifiable concentrate), were included in the study for comparison.

Algorithms↗
PubMed1992

Comparison of definitions of the lag phase and the exponential phase in bacterial growth.

Different definitions for the lag time and of the duration of the exponential phase can be used to calculate these quantities from growth models. The conventional definitions were compared with newly proposed definitions. It appeared to be possible to derive values for the lag time and the duration of the exponential phase from the growth models and differences between the various definitions could be quantified. All the different values can be calculated from the growth parameters microm, lambda and alpha. Therefore, it appeared to be unnecessary to use complicated mathematical equations; simple equations were adequate. For the Gompertz model the conventional definition of the lag time did not differ appreciably from the newly proposed definition. The end-point of the exponential phase and thus the duration of the exponential phase differed considerably for the two definitions. For the logistic model the two definitions lead to considerable differences for all quantities. It is recommended that the conventional definition is used for calculating the lag time. For the duration of the exponential phase it is recommended that the new definition is used. The value can be calculated, however, directly from the conventional growth parameters.

Bacteria↗
PubMed1989

A clinical model for diagnosis of urinary tract infection in young women.

To develop a clinical model for diagnosis of bacterial urinary tract infection, we conducted a prospective study on 266 dysuric young women, 147 of whom had urinary tract infections. Five variables were found to be significant and independent correlates to bacterial urinary tract infection on logistic regression analysis: sexual activity, absence of vaginal discharge, short duration of complaints, leukocyturia, and hematuria. An algorithm combining the logistic model and a Gram-stained urine specimen, which was used in only a third of our patients, afforded a sensitivity of 86% and a specificity of 84%. The algorithm was validated in a second set of 166 dysuric women, 77 of whom had urinary tract infections. The algorithm led to a diagnosis of bacterial urinary tract infection with a sensitivity of 91% and specificity of 79%; the only laboratory test needed except for urinalysis was a Gram's stain of urine, obtained for 30% of the patients.

Adolescent↗
PubMed1993

Modeling the growth of Enterococcus faecium in bologna sausage.

A study to set up mathematical models which allow the prediction of Enterococcus faecium growth in bologna sausage (mortadella) was carried out. Growth curves were obtained at different temperatures (5, 6, 12, 15, 25, 32, 35, 37, 42, 46, 50, 52, and 55 degrees C). The Gompertz and logistic models, modified by Zwietering, were found to fit with the representation of experimental curves. The variations of the parameters A (i.e., the asymptotic value reached by the relative population during the stationary growth phase), mu m (i.e., the maximum specific growth rate during the exponential growth phase), and lambda (i.e., the lag time) with temperature were then modeled. The variation of A with temperature can be described by an empirical polynomial model, whereas the variation of mu m and lambda can be described by the Ratkowsky model modified by Zwietering and the Adair model, respectively. Data processing of these models has shown that the minimum growth temperature for E. faecium is 0.1 degrees C, the maximum growth temperature is 53.4 degrees C, and the optimal growth temperature is 42 to 45 degrees C.

Animals↗
PubMedDate not supplied

The impact of insurance on access to physician services for elderly people with arthritis.

The impact of insurance on access to physician services among elderly individuals with chronic illnesses has far-reaching policy implications. Using a national probability sample of aged Medicare beneficiaries (N = 5,543), and controlling for severity of illness, comorbidities, and other covariates, we analyze this issue for the most prevalent, chronic disabling disease among the elderly: arthritis. The results from the two-part multivariate model (logistic regression followed by ordinary least squares regression) suggest that insurance status is a positive and statistically significant predictor of both initial access to care (p < .01), and amount of arthritis care used (p < .05). Taking the results of the two-part model, we conducted a microsimulation to estimate the increase in Medicare spending that would result if various types of Medicare supplemental insurance were provided to those who had none. Results suggest that Medicare expenditures would rise from $51 million to $59 million annually depending on the type of supplement provided.

Activities of Daily Living↗
PubMed1977

The combined effect of breast cancer risk factors.

An extension of the logistic model (Cox, 1970) is applied to the prospective study of breast cancer in Guernsey (Bulbrook and Hayward, 1967). Four important risk factors, age at menarche, family history, age at first birth and etiocholanolone excretion, are identified and shown to have additive effects on a logistic scale for the probability of developing breast cancer. The feasibility of screening a high risk group of women is considered and shown unlikely to be of practical value.

Adult↗
PubMed2007

Modeling the growth of the Goettingen minipig.

The Goettingen minipig developed at the University of Goettingen, Germany, is a special breed for medical research. As a laboratory animal it has to be as small and light as possible to facilitate handling during experiments. For achieving the breeding goal of small body size in the future, the growth pattern of the minipig was studied. This study deals with the analysis of minipig BW by modeling growth with linear and nonlinear functions and comparing the growth of the minipigs with that of normal, fattening pigs. Data were provided by Ellegaard Goettingen minipigs, Denmark, where 2 subpopulations of the Goettingen basis population are housed. In total 189,725 BW recordings of 33,704 animals collected from birth (d 0) to 700 d of age were analyzed. Seven nonlinear growth functions and 4 polynomial functions were applied. The growth models were compared by using the Akaike's information criterion (AIC). Regarding the whole growth curve, linear polynomials of third and fourth order of fit had the smallest AIC values, indicating the best fit for the minipig BW data. Among the nonlinear functions, the logistic model had the greatest AIC value. A comparison with fattening pigs showed that the minipigs have a nearly linear BW development in the time period from birth to 160 d. Fattening pigs have very low weight gains in their first 7 wk in relation to a specific end weight. After 7 wk, fattening pigs have increased growth, resulting in a growth curve that is more sigmoid than the growth curve of the minipig. Based on these results, further studies can be conducted to analyze the growth with random regression models and to estimate variance components for optimizing the strategies in minipig breeding.

Aging↗
PubMed1997

Validation of a predictive model of idiopathic membranous nephropathy: its clinical and research implications.

Although a number of factors have consistently correlated with progression to chronic renal insufficiency (CRI) in idiopathic membranous glomerulonephropathy (IMGN), they appear late, are not quantitative in nature and have not been validated. We have determined that the highest sustained six-month period of proteinuria is an important predictor of progression. Using multiple logistic modelling, the only additional prognostic variables of importance in 184 Canadian patients were the initial creatinine clearance and the rate of change in function over this six-month interval. Independent data from Italy (101 patients) and Finland (78 patients) were obtained for comparison. Sensitivity, specificity, negative and positive predictive values and overall accuracy, as well as Pearson's goodness-of-fit and Harrell's "C" statistic were used to assess the fits of the model. Accuracy of prediction was > or = 85% in all three countries. Pearson's Chi-square goodness-of-fit showed good agreement across the spectrum and Harrell's "C" statistic was > or = 90%. Therefore, a predictive, semiquantitative algorithm in IMGN has been validated. Its relevance in patient management and in clinical trials is illustrated.

Algorithms↗
PubMed2004

Robust Bayesian decision theory applied to optimal dosage.

We give a model for constructing an utility function u(theta,d) in a dose prescription problem. theta and d denote respectively the patient state of health and the dose. The construction of u is based on the conditional probabilities of several variables. These probabilities are described by logistic models. Obviously, u is only an approximation of the true utility function and that is why we investigate the sensitivity of the final decision with respect to the utility function. We construct a class of utility functions from u and approximate the set of all Bayes actions associated to that class. Then, we measure the sensitivity as the greatest difference between the expected utilities of two Bayes actions. Finally, we apply these results to weighing up a chemotherapy treatment of lung cancer. This application emphasizes the importance of measuring robustness through the utility of decisions rather than the decisions themselves.

Antineoplastic Agents↗
PubMed2004

Population models of sperm-dependent parthenogenesis.

Organisms that reproduce by sperm-dependent parthenogenesis are asexual clones that require sperm of a sexual host to initiate egg production, without the genome of the sperm contributing genetic information to the zygote. Although sperm-dependent parthenogenesis has some of the disadvantages of sex (requiring a mate) without the counterbalancing advantages (mixing of parental genotypes), it appears amongst a wide variety of species. We develop initial models for the density-dependent dynamics of animal populations with sperm-dependent parthenogenesis (pseudogamy or gynogenesis), based on the known biology of the common Enchytraeid worm Lumbricillus lineatus. Its sperm-dependent parthenogenetic populations are reproductive parasites of the hermaphrodite sexual form. Our logistic models reveal two alternative requirements for coexistence at density-dependent equilibria: (i) If the two forms differ in competitive ability, the form with the lower intrinsic birth rate must be compensated by a more than proportionately lower competitive impact from the other, relative to intraspecific competition, (ii) If the two forms differ in their intrinsic capacity to exploit resources, the sperm-dependent parthenogen must be superior in this respect and must have a lower intrinsic birth rate. In general for crowded environments we expect a sperm-dependent parthenogen to compete strongly for limiting resources with the sexual sibling species. Its competitive impact is likely to be weakened by its genetic uniformity, however, and this may suffice to cancel any advantage of higher intrinsic growth rate obtained from reproductive investment only in egg production. We discuss likely thresholds of coexistence for other sperm-dependent parthenogens. The fish Poeciliopsis monacha-lucida likewise obtains an intrinsic growth advantage from reduced investment in male gametes, and so its persistence is likely to depend on it being a poor competitor. The planarian Schmidtea polychroa obtains no such intrinsic benefit because it produces fertile sperm, and its persistence may depend on superior resource exploitation.

Animals↗
PubMed2003

Hostility during admission interview as a short-term predictor of aggression in acute psychiatric male inpatients.

BACKGROUND: A critical step for improving the prediction of on-ward violence is the identification of variables that are not only consistently associated with an increased risk of aggression but also easily evaluated during the admission interview. The goal of this prospective study was to assess the predictive utility of hostility during admission interview. METHOD: The sample consisted of 80 newly admitted male patients with heterogeneous DSM-IV psychiatric diagnoses recruited from the psychiatric ward of an urban public hospital. Psychiatric symptoms at admission were assessed with the Brief Psychiatric Rating Scale (BPRS). Aggressive behavior during the first week of hospitalization was measured with the Modified Overt Aggression Scale. Data were collected between January and June 1998. RESULTS: In a multiple regression model, BPRS items hostility and tension-excitement emerged as significant predictors of verbal aggression, whereas thinking disturbance (high) and suspiciousness-uncooperativeness (low) emerged as significant predictors of aggression against objects. In contrast, when aggression was treated as a binary dependent variable in a logistic model, hostility during the admission interview had no utility in predicting on-ward aggressive behavior. CONCLUSION: This study confirms the importance of distinguishing between different types of aggression to improve the accuracy of predictions of violence. The findings suggest that the question whether hostility is a useful short-term predictor of aggression in psychiatric inpatients cannot be answered conclusively. The predictive utility of hostility was relatively high for predicting verbal aggression but was negligible for predicting other types of aggressive behavior.

Acute Disease↗
PubMed1985

The risk of low birth weight. Alternative models of neonatal mortality.

The authors examine the use of the infant's weight at birth to estimate its risk of mortality by the 28th day of life. The performance of several commonly employed statistical models is compared for the population of single births to resident South Carolina mothers in 1975-1980. A log-linear function, fitting the natural logarithm of the probability of neonatal mortality to birth weight, performs far better in this analysis than a quadratic or a logistic model or a model using the logarithm of the probability of survival. The parsimonious log-linear model also appears preferable to more complex models with additional parameters. The authors use the model in an analysis of data in two-year periods to demonstrate its value as an indicator of underlying changes in neonatal prospects and its easily interpreted parameters. The results highlight the importance of changes in neonatal mortality affecting low birth weight infants, which produce a noticeable shift in the range in which low birth weight is associated with the risk of mortality. These have proven more important in accounting for the decline in mortality rates than have changes affecting only neonates with more typical birth weights in South Carolina in 1975-1980.

Birth Certificates↗
PubMed2000

The boundary for growth of Zygosaccharomyces bailii in acidified products described by models for time to growth and probability of growth.

Models to predict days to growth and probability of growth of Zygosaccharomyces bailii in high-acid foods were developed, and the equations are presented here. The models were constructed from measurements of growth of Z. bailii using automated turbidimetry over a 29-day period at various pH, NaCl, fructose, and acetic acid levels. Statistical analyses were carried out using Statistical Analysis Systems LIFEREG procedures, and the data were fitted to log-logistic models. Model 1 predicts days to growth based on two factors, combined molar concentration of salt plus sugar and undissociated acetic acid. This model allows a growth/no-growth boundary to be visualized. The boundary is comparable with that established by G. Tuynenburg Muys (Process Biochem. 6:25-28, 1971), which still forms the basis of industry assumptions about the stability of acidic foods. Model 2 predicts days to growth based on the four independent factors of salt, sugar, acetic acid, and pH levels and is, therefore, much more useful for product development. Validation data derived from challenge studies in retail products from the U.S. market are presented for Model 2, showing that the model gives reliable, fail-safe predictions and is suitable for use in predicting growth responses of Z. bailii in high-acid foods. Model 3 predicts probability of growth of Z. bailii in 29 days. This model is most useful for spoilage risk assessment. All three models showed good agreement between predictions and observed values for the underlying data.

Food Microbiology↗
PubMed1976

A computer program suitable for fitting linear models when the dependent variable is dichotomous, polichotomous or censored survival and non-linear models when the dependent variable is quantitative.

Given a set of measurements of s explanatory variables corresponding to each experimental unit, a computer program, whose methodological background can be found in [2] has been written in FORTRAN IV language in order to perform regression analyses when the dependent variable is: (i) dichotomous; (ii) polichotomous; (iii) censored survival. In the two former the Cox's [6] linear logistic models are used while in the third one it has been resorted to the models suggested by Feigl and Zelen [8]. The statistical estimation procedure is maximum likelihood and among the different algorithms developed to reach this goal, the one published by Van der Voort and Dorpema [3], has been utilized. Furthermore, when the dependent variable is quantitative, the program is suitable to fit any function non-linear in the parameters; the pertinent function and its first and second derivatives must be provided by the user. In the present version, implemented on a Univac 1106 machine, the program fits directly the Gompertz function.

Computers↗
PubMed1988

Analysis of geographic differentials in infant mortality rates. The Or Yehuda community.

Comprehensive evaluation of matched infant death certificate data and livebirth certificate data for 1977-1980 was performed for two areas in Israel: Or Yehuda, a small, low socioeconomic status community which had an infant mortality rate of 19.1 per 1,000, and the rest of Ramat Gan district, which had an infant mortality rate of 10.3 per 1,000. A method is presented which illuminates the role of statistical models in analyzing small area data, in evaluating twofold observed differences in crude and factor-specific mortality rates in two areas, in assessing heterogeneity in population stratum-specific mortality rate ratios, and in identifying causes for inter-area differences in infant mortality rate. Identical logistic models were fitted to each of the areas independently, and these were used to investigate effects due to birth weight, sex, parity, maternal age and education, and parental occupation. The differences in the distribution of risk level (number of risk factors) present in each population (or the proportion of multi-problem families) were identified as a single factor that can explain most of the disparity between the areas. The direction and magnitude of the relation between risk level and infant mortality rate were similar in both communities: the greater the number of risk factors, the higher the rate. Identification of a target population for intervention through only one or two specific risk factors would be unprofitable in reducing the overall community infant mortality rate since too many families with multiple risk would be excluded, and too many with single risk factors would be included.

Adult↗
PubMedDate not supplied

Clinical signs and symptoms in the assessment of immunodeficiency in men with subtype C HIV infection in Harare, Zimbabwe.

PURPOSE: Providing low-cost interventions such as co-trimoxazole as prophylaxis against opportunistic infections among HIV-infected individuals depends on the identification of those at risk. This article describes the prevalence of self-reported signs and symptoms and CD4 cell counts in a cohort of 447 HIV seropositive men. A scoring system using self-reported signs and symptoms was developed and tested in the prediction of low CD4 cell counts. This approach may allow health care providers in low-resource settings to predict severe immunodeficiency and to provide care. METHOD: Data on clinical manifestations of HIV infection and blood samples for HIV serology were collected prospectively from an ambulatory cohort of men seen at their workplace at enrollment and every 6 months thereafter. CD4+ cell counts were obtained on samples testing positive on ELISA. Using data reduction techniques and logistic modeling, we developed a prognostic score system. RESULTS: 20% of the men had CD4+ cell counts below 200. All reported signs and symptoms were more frequent in men with less than 200 CD4+ cell counts compared to men with CD4+ cell counts greater than 200. History of malaria, fever, lymphadenopathy, persistent diarrhea, persistent cough, and skin infections robustly predicted low CD4+ count. A scoring system equation was developed based on the coefficients of the multivariate logistic regression: 1x(tuberculosis) + 3.2x(herpes zoster) + 4.5x(malaria) + 5.7x(fever) + 5.8x(cough) + 8.2x(lymphadenopathy) + 8.5x(skin infection). Setting the score cutoff value greater than or equal 5, the model had moderately high sensitivity of 61% and specificity of 72%. The scoring system had an overall classification error rate of 30%. CONCLUSION: By using this simple scoring system, physicians can correctly identify 72% of patients who do not require immediate intervention, thereby channeling scarce resources to those who have both low CD4+ cell counts and symptoms and are most likely to benefit from prophylactic and antiretroviral interventions.

AIDS-Related Opportunistic Infections↗
PubMed1989

Susceptibility of Eimeria bovis and Toxoplasma gondii to oxygen intermediates and a new mathematical model for parasite killing.

Eimeria bovis and Toxoplasma gondii differ in their susceptibility to macrophages activated by lymphokines. Interferon-gamma can activate macrophages to totally inhibit E. bovis sporozoite development, whereas growth of T. gondii tachyzoites in macrophages is not totally affected. The susceptibility of these parasites to oxygen intermediates and their ability to evade the oxidative burst by macrophages were investigated in cell-free systems. Using a logistic model to assess growth inhibition, T. gondii growth was impaired by 50% at 10(-4.25) M (56 microM) H2O2, with 30 min as the optimum time for measuring inhibition. Preliminary results indicate that T. gondii follows mode-one and mode-two killing with relation to time after exposure to H2O2, implying a role for OH. and the induction of a DNA repair mechanism. The same model was used to assess inhibition of E. bovis growth that was more susceptible, being inhibited to 50% by 10(-5) M (10 microM) H2O2. Both parasites were susceptible to the effects of xanthine-xanthine oxidase that releases a full complement of oxygen intermediates (H2O2, OH., (1)O2, and O2-). Adding quenchers or scavengers to the system confirmed that T. gondii was susceptible to products of the interaction of O2- and H2O2 (OH. and (1)O2), and that E. bovis sporozoites were at least partially susceptible to H2O2 and O2-, but extremely susceptible to OH.. These data were supported by studies on scavenging enzymes present in the parasites. Toxoplasma gondii was rich in superoxide dismutase (SOD), catalase, and glutathione peroxidase (GPO), and E. bovis had less catalase and SOD.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2003

[Effects of a comprehensive health education program on reproductive tract infections/sexually transmitted diseases intervention among reproductive age population in the rural areas of China].

OBJECTIVE: To evaluate the effectiveness on comprehensive health education intervention program regarding reproductive tract infections/sexually transmitted diseases (RTIs/STDs) among reproductive age population in the rural areas of China. METHODS: Data were generated from the Reproductive Health/Family Planning Project implemented by the State Family Planning Committee and the Ministry of Health from 1998 to 2002, which covered 32 counties in 22 provinces. A quasi-experimental design was used. Six counties were selected from 32 project counties as intervention group, while 6 non-project counties were taken as controls which were similar in number of population and economic level to the counties as selected. Subjects of the study were mothers with children under 3 years and men under 35 years of age. A total number of 675 mothers and men were interviewed using a structured questionnaire by strictly trained investigators. Logistic model was used to compare the difference of knowledge on RTIs/STDs between intervention group and control group. OR value was used to describe the degree of the difference. RESULTS: Over the 18 month intervention period, persons in the intervention group had more knowledge of RTIs/STDs than those in control group. Logistic regression analysis indicated that intervention was significantly associated with better knowledge on factors as transmission, risks, symptoms, management and prevention of RTIs/STDs with 95% CI of OR as 2.4 - 6.4, 2.0 - 4.8, 3.0 - 6.4, 1.9 - 5.7 and 1.8 - 6.8 respectively, after controlling the demographic factors. Level of education was an important factor influencing the subjects to receive knowledge on RTIs/STDs. CONCLUSION: Comprehensive health education intervention programs had significant impact on knowledge about RTIs/STDs among the target population, indicating that the Reproductive Health/Family Planning Project implemented in the rural areas of China had been successful.

Adult↗