Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Statistical Regression”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,045 records · Page 58Linked to original sources
PubMed2001

HTLV-1 and HTLV-2 infections in HIV-infected individuals from Santos, Brazil: seroprevalence and risk factors.

Because HTLV-I, HTLV-2, and HIV share identical modes of transmission, simultaneous or subsequent infections with these retroviruses are to be expected. The population of Santos, the largest port in Latin America, includes large numbers of female commercial sex workers and intravenous drug users, presumably having been exposed to retroviral infection. To evaluate the seroprevalence of HTLV infection and their associated risk factors, a cross-sectional survey was carried out in 499 HIV-infected individuals from Santos, Brazil. HTLV testing consisted of enzyme immunoassays for serologic screening and confirmatory Western blot testing. Overall HTLV-I and HTLV-2 seroprevalences were 6.0% (95% confidence interval [CI], 3.9-8.1) and 7.4% (95% CI, 5.1-9.7), respectively. Multivariate logistic regression for statistical analysis revealed HTLV-I infection to be independently associated with: intravenous drug use (IDU) (odds ratio [OR]. 2.99; 95% CI, 1.09-8.20), seropositivity to hepatitis C virus (HCV) (OR, 3.03; 95% CI, 1.02-9.01) and < 3 years of education (OR, 4.73; 95% CI, 1.56-14.41). HTLV-2 infection was associated with: IDU (OR, 3.22; 95% CI, 1.33-7.84), HCV seropositivity (OR, 5.40; 95% CI, 1.86-15.66) and nonwhite race (OR, 3.32; 95% CI, 1.58-7.00). Results indicate that HIV-infected individuals living in Santos are at similarly high risk of being exposed to HTLV-1 and HTLV-2. IDU constitutes the main risk factor for HTLV acquisition in this population, and there is no significant risk associated with sexual practice.

Adolescent↗
PubMed1991

A note on the conditional approach to interval estimation in the calibration problem.

In the calibration problem, the need to construct a confidence interval to estimate the unknown chi 0 arises when the null hypothesis of zero slope is rejected. Otherwise, the resulting confidence interval will be infinite to reflect the fact that the slope of the regression line may be zero. Under the condition of rejecting the hypothesis of zero slope, we study the properties of the conditional coverage rate of the calibration confidence interval. The conditional coverage rate (P1) is a function of the slope, distance between chi 0 and the mean of the trailing sample means, the sum of squares of chi, and n. When the true slope is close to 0 and chi 0 is away from means, P1 can go down to 0. On the other hand, as the power of testing zero slope reaches 1, with or without chi 0 close to means, P1 will tend to the desired nominal coverage rate. In summary, one should choose a reasonably small alpha in testing zero slope to avoid constructing a confidence interval for chi 0 when the true slope is 0. In addition, it is desirable to have high power in testing zero slope so that the resulting confidence interval will maintain the desired coverage rate when using the conditional approach in the calibration problem.

Biometry↗
PubMed2000

Measuring hospital efficiency: a comparison of two approaches.

OBJECTIVE: To compare the results of scoring hospital efficiency by means of two new types of frontier models, Data Envelopment Analysis (DEA) and stochastic frontier regression (SFR). STUDY SETTING: Financial records of Florida acute care hospitals in continuous operation over the period 1982-1993. STUDY DESIGN: Comparable DEA and SFR models are specified, and these models are then estimated to obtain the efficiency indexes yielded by each. The empirical results are subsequently examined to ascertain the extent to which they serve the needs of hospital policymakers. DATA COLLECTION: A longitudinal or panel data set is assembled, and a common set of output, input, and cost indicators is constructed to support the estimation of comparable DEA and SFR models. PRINCIPAL FINDINGS: DEA and SFR models yield convergent evidence about hospital efficiency at the industry level, but divergent portraits of the individual characteristics of the most and least efficient facilities. CONCLUSIONS: Hospital policymakers should not be indifferent to the choice of the frontier model used to score efficiency relationships. They may be well advised to wait until additional research clarifies reasons why DEA and SFR models yield divergent results before they introduce these methods into the policy process.

Bed Occupancy↗
PubMed1989

Empirical comparisons of proportional hazards and logistic regression models.

We compare parameter estimates from the proportional hazards model, the cumulative logistic model and a new modified logistic model (referred to as the person-time logistic model), with the use of simulated data sets and with the following quantities varied: disease incidence, risk factor strength, length of follow-up, the proportion censored, non-proportional hazards, and sample size. Parameter estimates from the person-time logistic regression model closely approximated those from the Cox model when the survival time distribution was close to exponential, but could differ substantially in other situations. We found parameter estimates from the cumulative logistic model similar to those from the Cox and person-time logistic models when the disease was rare, the risk factor moderate, and censoring rates similar across the covariates. We also compare the models with analysis of a real data set that involves the relationship of age, race, sex, blood pressure, and smoking to subsequent mortality. In this example, the length of follow-up among survivors varied from 5 to 14 years and the Cox and person-time logistic approaches gave nearly identical results. The cumulative logistic results had somewhat larger p-values but were substantively similar for all but one coefficient (the age-race interaction). The latter difference reflects differential censoring rates by age, race and sex.

Adolescent↗
PubMed1993

Allosterism and Na(+)-D-glucose cotransport kinetics in rabbit jejunal vesicles: compatibility with mixed positive and negative cooperativities in a homo- dimeric or tetrameric structure and experimental evidence for only one transport protein involved.

We first present two simple dimeric models of cotransport that may account for all of the kinetics of Na(+)-D-glucose cotransport published so far in the small intestine. Both the sigmoidicity in the Na+ activation of transport (positive cooperativity) and the upward deviations from linearity in the Eadie-Hofstee plots relative to glucose concentrations (negative cooperativity) can be rationalized within the concept of allosteric kinetic mechanisms corresponding to either of two models involving sequential or mixed concerted and sequential conformational changes. Such models also allow for 2 Na+: 1 S and 1 Na+: 1 S stoichiometries of cotransport at low and high substrate concentrations, respectively, and for partial inhibition by inhibitors or substrate analogues. Moreover, it is shown that the dimeric models may present physiological advantages over the seemingly admitted hypothesis of two different cotransporters in that tissue. We next address the reevaluation of Na(+)-D-glucose cotransport kinetics in rabbit intestinal brush border membrane vesicles using stable membrane preparations, a dynamic approach with the Fast Sampling Rapid Filtration Apparatus (FSRFA), and both nonlinear regression and statistical analyses. Under different conditions of temperatures, Na+ concentrations, and membrane potentials clamped using two different techniques, we demonstrate that our data can be fully accounted for by the presence of only one carrier in rabbit jejunal brush border membranes since transport kinetics relative to glucose concentrations satisfy simple Michaelis-Menten kinetics. Although supporting a monomeric structure of the cotransporter, such a conclusion would conflict with previous kinetic data and more recent studies implying a polymeric structure of the carrier protein. We thus consider a number of alternatives trying to reconcile the observation of Michaelis-Menten kinetics with allosteric mechanisms of cotransport associated with both positive and negative cooperativities for Na+ and glucose binding, respectively. Such models, implying energy storage and release steps through conformational changes associated with ligand binding to an allosteric protein, provide a rational hypothesis to understand the long-time debated question of energy transduction from the Na+ electrochemical gradient to the transporter.

Allosteric Regulation↗
PubMed2002

Detecting gene-gene interactions using affected sib pair analysis with covariates.

Interest has recently focussed on allowing for interactions between loci as a way to increase power to detect linkage. In this paper, a simplified logistic regression method was used to perform affected sib pair analyses allowing for the inclusion of data from other loci. A systematic search of two-locus disease models was carried out to determine the situations in which this was advantageous. If IBD information is available (e.g. from a genome scan), it is unlikely that allowing for interactions will give a large lod score in the absence of linkage evidence from sinlge-locus analysis. Furthermore, allowing for interactions rarely gave a significant increase in power to detect linkage over a single-locus analysis, except for heterogeneity models with low K(P). Conversely, the availability of disease-associated genotypes may greatly increase the power both to detect linkage to a second locus and interaction between the loci. These results indicate that when only IBD information is available, two-locus analysis of genome scan data should be restricted to regions giving peaks under single-locus analysis. If disease-associated genotypes are available, it may be worth re-analysing the whole genome.

Genetic Linkage↗
PubMed1990

Towards developing a diagnostic algorithm for Chlamydia trachomatis and Neisseria gonorrhoeae cervicitis in pregnancy.

C trachomatis and N gonorrhoeae are major causes of maternal and neonatal morbidity and mortality in developing countries. To identify characteristics predictive of cervical infection, we examined pregnant women attending an antenatal clinic in Nairobi, Kenya. C trachomatis was isolated from 14/178 (8%), and N gonorrhoeae from 17 (10%); cervical infection with either pathogen was present in 28 (16%). Two characteristics were independently predictive of cervical infection by logistic regression analysis; the presence of either endocervical mucopus or induced endocervical bleeding, relative risk 4.2 (95% confidence interval (CI) 2.2 to 8.0) and having more than one sexual partner during pregnancy, relative risk 3.3 (95% CI 1.4 to 7.6). A screening programme for cervical infection which tested women with one or both risk markers would have a sensitivity of 68% (95% CI 51 to 85%) and a positive predictive value of 0.35 (95% CI 0.22 to 0.47). In countries where resources are limited, diagnostic algorithms incorporating clinical signs and behavioural characteristics may be useful in identifying pregnant women at high risk of cervical infection.

Adult↗
PubMed1986

Comparison of biparietal diameter and femur length in the third trimester: effects of gestational age and variation in fetal growth.

A multiple regression-based statistical model capable of quantitatively comparing two or more sonographic parameters for the effects of gestational age, variation in fetal growth and error in sonographic measurement is presented and then used to compare the biparietal diameter and femur length as estimators of gestational age in late pregnancy. A total of 311 patients were studied between 24 and 42 weeks' gestation. Variation in fetal growth was expressed as the birth weight percentile for gestational age. Biparietal diameter and femur length correlated equally well with gestational age. However, the biparietal diameter was more than twice as sensitive as the femur length to variation in fetal growth. Femur length had a larger error associated with its measurement. These results suggest that the biparietal diameter and femur length in late pregnancy are equal estimators of gestational age; that the femur length is a more stable estimator of gestational age when fetal growth deviates from normal; and that the femur length is technically more difficult to obtain.

Birth Weight↗
PubMed2002

Validation of the urgency algorithm for near-side crashes.

The URGENCY algorithm uses vehicle crash sensor data in Automatic Crash Notification (ACN) systems to assist in instantly identifying crashes that are most likely to have time critical injuries. The algorithm also provides the capability of improving injury identification, using data obtained from the scene. The prime purpose of the algorithm is to automatically provide emergency medical responders with objective information on crash severity to assist in detecting the approximately 1% of crashes with serious injuries needing the most urgent medical care. The algorithm calculates the risk of a MAIS 3+ injury being present in the crashed vehicle, instantly at the time of the crash. The prediction can be subsequently updated as more information becomes available. The algorithm was based on a multiple regression analysis using data from the National Accident Sampling System/Crashworthiness Data System, (NASS/CDS) years 1988-95. In this paper, the accuracy of the algorithm was evaluated for near side crashes by applying it retrospectively to the population of injured occupants in NASS 1997-2000. URGENCY was applied to the population of injured occupants in near side crashes. Using an injury risk criterion of 50%, URGENCY identified 69% of the crashes with MAIS 3+ injuries. By lowering injury risk criterion to 40%, URGENCY identified 78% of the crashes with MAIS 3+ injuries. Vehicle side intrusion was found to be a highly influential variable. By changing side intrusion from a binary to a continuous variable, the correctly identified crashes increased from 69% to 81%. Examination of the consequence of missing variables found that unknown values of occupant height and weight had a negligible effect on the ability to capture the MAIS 3+ injured. However, lack of knowledge of these variables did increase the magnitude of the false positives.

Accidents, Traffic↗
PubMed1992

The risk approach to intervention in severe malnutrition in rural Bangladesh.

To determine whether clinical marasmus occurs in small groups of children from easily recognizable high-risk households, the authors conducted a case-control study to identify risk indicators that may be used in targeted interventions. Cases were children whose mid-upper arm circumference measured less than 110 mm, and controls were children matched for age and sex with arm circumferences greater than 120 mm. Between June 1988 and June 1989, 164 such pairs of children aged 1-4 years were studied in Matlab, Bangladesh. Conditional logistic regression analysis showed an increased risk of marasmus among children from families with other children under 5 years of age (odds ratio = 2.80, 95% confidence interval 1.56-5.02) and children who consumed formula foods (odds ratio = 18.81, 95% confidence interval 4.15-85). Higher maternal education was associated with reduced risk of marasmus. Further examination of these risk indicators suggests that the resources saved through targeting fewer households will be negated by missing many children with marasmus. The authors conclude that the application of targeted interventions against marasmus, using the risk approach, is unlikely to be efficient.

Arm↗
PubMed1989

Censoring in an epidemic with an application to hemophilia-associated AIDS.

In epidemiologic studies of infectious diseases, the times of infection may be known only up to an interval. A two-stage parametric regression model is proposed for the analysis of cohort studies during an epidemic in which the exact times of infection cannot be ascertained. The methods permit joint estimation of the effects of covariates both on the risk of infection and the risk of progression to clinical disease once infected. The methodology is applied to a cohort of hemophiliacs who were at risk of infection with the AIDS virus. It was found that hemophiliacs with severe Type A hemophilia were at highest risk of infection, and the risk of infection increased sharply in the early 1980s. Hemophiliacs who were over the age of 20 at infection were at higher risk of progression to AIDS than hemophiliacs who were under age 20. The estimate of the cumulative probability of developing AIDS within t years of infection (the incubation period distribution) for hemophiliacs over age 20 was 1 - exp(-.0021t2.516). Since follow-up in this cohort was restricted to about 10 years from infection, estimates of the incubation period distribution beyond 10 years depend on model extrapolation and should be interpreted cautiously.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Sexual communication is associated with condom use by sexually active incarcerated adolescents.

PURPOSE: Incarcerated adolescents are at increased risk for infection by sexually transmitted diseases (STDs), including human immunodeficiency virus (HIV). Moreover, condom use by this population is extremely low. Although interpersonal variables such as sexual communication have been found to be associated with condom use in other populations, few researchers have investigated this relationship among adolescents requiring detention in juvenile facilities. The present study investigated the relationship between communication about sexual history and incarcerated adolescents' condom use. METHODS: We used multivariate logistic regression techniques to analyze interview data from a predominantly Latino sample of 2,132 sexually active adolescents detained in Los Angeles County Juvenile Hall. RESULTS: Despite high numbers of lifetime sexual partners, a substantial majority of respondents (67%) reported that they never used condoms during sexual intercourse. Respondents who communicated with their sex partner(s) about each others' sexual history were significantly more likely to use condoms during sexual intercourse. Adolescents who reported that they knew someone with AIDS were also more likely to use condoms. CONCLUSIONS: Interventions designed to increase condom use among sexually active incarcerated adolescents should include a component addressing sexual communication practices. More research is needed on the ways in which adolescents learn to communicate about sex.

Adolescent↗
PubMed2006

Bivariate line-fitting methods for allometry.

Fitting a line to a bivariate dataset can be a deceptively complex problem, and there has been much debate on this issue in the literature. In this review, we describe for the practitioner the essential features of line-fitting methods for estimating the relationship between two variables: what methods are commonly used, which method should be used when, and how to make inferences from these lines to answer common research questions. A particularly important point for line-fitting in allometry is that usually, two sources of error are present (which we call measurement and equation error), and these have quite different implications for choice of line-fitting method. As a consequence, the approach in this review and the methods presented have subtle but important differences from previous reviews in the biology literature. Linear regression, major axis and standardised major axis are alternative methods that can be appropriate when there is no measurement error. When there is measurement error, this often needs to be estimated and used to adjust the variance terms in formulae for line-fitting. We also review line-fitting methods for phylogenetic analyses. Methods of inference are described for the line-fitting techniques discussed in this paper. The types of inference considered here are testing if the slope or elevation equals a given value, constructing confidence intervals for the slope or elevation, comparing several slopes or elevations, and testing for shift along the axis amongst several groups. In some cases several methods have been proposed in the literature. These are discussed and compared. In other cases there is little or no previous guidance available in the literature. Simulations were conducted to check whether the methods of inference proposed have the intended coverage probability or Type I error. We identified the methods of inference that perform well and recommend the techniques that should be adopted in future work.

Algorithms↗
PubMed1990

Time from infection with HIV to onset of AIDS in patients with haemophilia in the UK.

The two-stage parametric regression model of Brookmeyer and Goedert has been adapted and fitted to data on the development of AIDS in haemophiliacs in the UK who are seropositive for HIV. The risk of developing AIDS by a given time following seroconversion increases with increasing age at seroconversion. It is likely that the risk increases smoothly with age, although the data have been analysed in three age categories, and it is estimated that by seven years after seroconversion 6 per cent of patients aged under 25 at seroconversion, 20 per cent of those aged 25-44 and 34 per cent of those aged 45 or more have developed AIDS. For a given age at seroconversion the annual risk of developing AIDS increases with increasing time after seroconversion, and at seven years the annual risks of developing AIDS during the next year in the three age groups are estimated to be 2 per cent for those aged less than 25 at seroconversion, and 10 and 11 per cent respectively for those aged 25-44 and 45 or more.

Acquired Immunodeficiency Syndrome↗
PubMed2006

Random regression models for male and female fertility evaluation using longitudinal binary data.

A longitudinal Bayesian threshold analysis of insemination outcomes was carried out using 2 random regression models with 3 (Model 1) and 5 (Model 2) parameters to model the additive genetic values at the liability scale. All insemination events of first-parity Holstein cows were used. The outcome of an insemination event was treated as a binary response of either a success (1) or a failure (0). Thus, all breeding information for a cow, including all service sires, was included, thereby allowing for a joint evaluation of male and female fertility. An edited data set of 369,353 insemination records from 210,373 first-lactation cows was used. On the liability scale, both models included the systematic effects of herd-year, month of insemination, technician, and regressions on age of service sire and milk yield during the first 100 d of lactation. The random effects in the model were the 3 or 5 random regression coefficients specific to each cow, the permanent effect of the cow, and the service sire effect. Using Model 1, the estimated heritability of an insemination outcome decreased from 0.035 at d 50 to 0.032 at d 140 and then increased continuously with DIM. The genetic correlations for insemination success at different time points ranged from 0.83 to 0.99, and their magnitude decreased with an increase in the interval between inseminations. A similar trend was observed for heritability and genetic correlations using Model 2. However, the average estimate of heritability was much higher (0.058) than those obtained using Model 1 or a repeatability model. In addition, the estimated genetic correlations followed the same trend as Model 1, but were lower and with a higher rate of decrease when the interval between inseminations increased. The posterior mean of service sire variance was 0.01 for both models, and permanent environmental variance was 0.05 and 0.02 for Models 1 and 2, respectively. Model comparison based on the Bayes factor indicated that Model 1 was more plausible, given the data.

Animals↗
PubMed2006

Regression as a method to predict copy numbers in comparative genomic hybridization studies on bacteria.

Comparative genomic hybridizations (CGH) using microarrays are performed with bacteria in order to determine the level of genomic similarity between various strains. The microarrays applied in CGH experiments are constructed on the basis of the genome sequence of one strain, which is used as a control, or reference, in each experiment. A strain being compared with the known strain is called the unknown strain. The ratios of fluorescent intensities obtained from the spots on the microarrays can be used to determine which genes are divergent in the unknown strain, as well as to predict the copy number of actual genes in the unknown strain. In this paper, we focus on the prediction of gene copy number based on data from CGH experiments. We assumed a linear connection between the log2 of the copy number and the observed log2-ratios, then predictors based on the factor analysis model and the linear random model were proposed in an attempt to identify the copy numbers. These predictors were compared to using the ratio of the intensities directly. Simulations indicated that the proposed predictors improved the prediction of the copy number in most situations. The predictors were applied on CGH data obtained from experiments with Enterococcus faecalis strains in order to determine copy number of relevant genes in five different strains.

Algorithms↗
PubMed1992

Sexual behavior and status for human immunodeficiency virus type 1 among homosexual and bisexual males in Mexico City.

The authors examined sexual behaviors, the seroprevalence of human immunodeficiency virus type 1 (HIV-1), and condom use among 2,314 homosexual and bisexual men tested during 1988-1989 at the AIDS (acquired immunodeficiency syndrome) National Center in Mexico City. Bisexuals constituted 24% of the sample; the seroprevalence rate was lower for bisexuals than homosexuals (21 vs. 34%). In logistic regressions, HIV-1 seropositivity was independently related to age, education, pattern of insertive/receptive behavior in anal sex, lifetime number of male sex partners, having sex with someone with AIDS, homosexual versus bisexual behavior, and a history of condyloma. The same logistic regressions were found to fit bisexuals and homosexuals. The rate of HIV-1 was reduced in individuals who indicated always requiring their partners to use a condom when practicing receptive anal sex (1% of the total). The most common practice for both homosexuals and bisexuals was "mixed" behavior (i.e., both insertive and receptive anal sex); this was also the practice with the highest risk. Bisexuals practiced both vaginal and anal sex with women and reported little condom use. The substantial seroprevalence among bisexuals, their frequent sexual contact with women, and their low rate of condom use imply a continuing role as a bridge of infection to females. Whether this risk will lead to a sustained heterosexual epidemic remains to be determined.

Adolescent↗
PubMedDate not supplied

Success-failure on the National Council Licensure Examination for Registered Nurses by nurse candidates from an accelerated baccalaureate nursing program.

Nine years of data from first-time nurse candidates taking the National Council Licensure Examination for Registered Nurses (NCLEX-RN) were examined to identify predictors of successful performance and determine probabilities of success. Using logistic regression, four statistical models at strategic time periods during an accelerated baccalaureate nursing program were tested to see when intervention might be initiated to influence student performance on the NCLEX-RN. By the end of the first semester the model could predict failure for 94 per cent of those who failed, but it was less consequential in correctly predicting success of those who passed. Significant variables placing nurse candidates at risk included their first-semester grade point average, sex, and whether they were foreign educated. By the end of the second semester, with each full letter grade increase in cumulative grade point average, nurse candidates had a 46 times better chance of passing the NCLEX-RN; American-educated nurse candidates had a 4.5 times better chance of passing than their foreign-educated counterparts. At the end of the final semester, with each full letter grade increase on the final cumulative grade point average, nurse candidates had a 97 times greater likelihood of performing successfully on the NCLEX-RN.

Achievement↗