PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Models, Statistical”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 37 records · Page 2Linked to original sources
PubMed1991

Empirical evaluation of statistical models for counts or rates.

We consider methods for selecting the joint specification of the mean and variance functions in statistical models for rates or counts. Based on analyses of diagnosis-specific hospital discharge rates in Michigan, we show that a Poisson model with an extra variance component for the systematic variation is superior to several other probability models with regard to specification of the error structure. Further, the deviance residual appears superior to the Pearson residual. The proper specification of such variation is crucial for many types of analyses, such as identification of outliers and regression analyses designed to explain the systematic component of the variation.

Analysis of Variance↗
PubMed1991

Use of brain biopsy for diagnostic evaluation of patients with suspected herpes simplex encephalitis: a statistical model and its clinical implications. NIAID Collaborative Antiviral Study Group.

Using the decision analysis technique and multivariate regression methods, a statistical model was established to define the utility of brain biopsy for diagnostic evaluation of patients with suspected herpes simplex encephalitis (HSE). Two strategies were compared: strategy I, brain biopsy with acyclovir (ACV) treatment for 10 days in biopsy-positive patients, and strategy II, ACV therapy without brain biopsy. Strategy I resulted in a greater 6-month survival rate when the likelihood of patients having HSE was less than 70%. Based on the current estimated prevalence of HSE (for patients with suspected HSE) of 35%, strategy I showed a slight advantage of a 3.2% increase in 6-month survival rate. An individual patient's chance of a positive brain biopsy can be predicted using a mathematical equation based on several important clinical assessments. This equation in conjunction with the decision analysis is a useful guide for the clinical management of patients with regard to brain biopsy.

Acyclovir↗
PubMed1992

Statistical model to determine the relationship of response and survival in patients with advanced ovarian cancer treated with chemotherapy.

BACKGROUND: A statistically appropriate analysis of the association between survival and response measures in patients with ovarian cancer could help to define the role of response rate in planning, monitoring, and interpreting the results of clinical trials. PURPOSE: This study was designed to investigate the relationship between antitumor response determined by clinical or pathological means and survival in patients with advanced ovarian cancer with no previous treatment. We focused on avoiding the limitations of the usual approach of comparing durations of survival for patients responding to therapy with those for nonresponders. METHODS: A new meta-analytic statistical model we developed was used to analyze data from 26 randomized clinical trials published between 1975 and 1989. Our model incorporates intra-study and inter-study sources of variability in the estimates of response and survival. The study also addresses the methodological problems of evaluating response as a surrogate end point and the relevance of this association to clinical decision making and the design of clinical trials. RESULTS: For 13 studies in which response was pathologically assessed, an improvement in surgically documented complete response rate was associated with an increase in median survival. A similar but apparently smaller effect was found for the association between objective clinical response and median survival in the 25 studies reporting these data. CONCLUSIONS: These results suggest that therapeutic measures must produce large improvements in clinical response rates to achieve meaningful effects on median survival. Improvement in surgically documented complete response rate appears to be more strongly associated with increased median survival and, hence, might be used for interim monitoring in clinical trials, but the role of second-look procedures in clinical management is controversial.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1991

The frequency of ion-pair substructures in proteins is quantitatively related to electrostatic potential: a statistical model for nonbonded interactions.

A statistical analysis of ion pairs in protein crystal structures shows that their abundance with respect to uncharged controls is accurately predicted by a Boltzmann-like function of electrostatic potential. It appears that the mechanisms of protein folding and/or evolution combine to produce a "thermal" distribution of local nonbonded interactions, as has been suggested by statistical-mechanical theories. Using this relationship, we develop a maximum likelihood methodology for estimation of apparent energetic parameters from the data base of known structures, and we derive electrostatic potential functions that lead to optimal agreement of observed and predicted ion-pair frequencies. These are similar to potentials of mean force derived from electrostatic theory, but departure from Coulombic behavior is less than has been suggested.

Biological Evolution↗
PubMedDate not supplied

[Variability in scabies mites Sarcoptes scabiei De Geer (Acariformes, Sarcoptidae) in relation to scabies epidemiology. 1. A statistical model of female variability].

Individual variability of 235 grain mite females from Moscow and the Moscow Province was studied. The data were processed on a computer. Body proportions were used as a representative dimension index. The size of proterosomal scutellum was stable. A map of the chaetoid cover of notum is given, and its variability was studied. Statistical analysis of all signs was made. Frontal chaetoid and sejugal sections and the number of caudal chaetoids are stable. Naked, middle and abdominal chaetoid sections are the most variable. Linear sizes of naked section and the number of chaetoid sets on middle and abdominal sections correlate with the number of undeveloped chaetoids. The statistical model of variability may be useful for populational analysis of Sarcoptes forms in connection with scab epidemiology.

Animals↗
PubMed2025

Inferring the sensitivity of wastewater metagenomic sequencing for early detection of viruses: a statistical modelling study.

BACKGROUND: Metagenomic sequencing of wastewater (W-MGS) can in principle detect any known or novel pathogen in a population. We aimed to quantify the sensitivity and cost of W-MGS for viral pathogen detection by jointly analysing W-MGS and epidemiological data for a range of human-infecting viruses. METHODS: In this statistical modelling study, we analysed sequencing data from four studies of untargeted W-MGS to estimate the relative abundance of 11 human-infecting viruses. Corresponding prevalence and incidence estimates were obtained or calculated from academic and public health reports. We combined these estimates using a hierarchical Bayesian model to predict relative abundance at set prevalence or incidence values, allowing comparison across studies and viruses. These predictions were then used to estimate the sequencing depth and concomitant cost required for pathogen detection using W-MGS with or without use of a hybridisation capture enrichment panel. FINDINGS: After controlling for variation in local infection rates, relative abundance varied by orders of magnitude across studies for a given virus. For instance, a local SARS-CoV-2 weekly incidence of 1% corresponded to a predicted SARS-CoV-2 relative abundance ranging from 3·8 × 10-10 to 2·4 × 10-7 across studies, translating to orders-of-magnitude variation in the cost of operating a system able to detect a SARS-CoV-2-like pathogen at a given sensitivity. Use of a respiratory virus enrichment panel in two studies greatly increased predicted relative abundance of SARS-CoV-2, lowering yearly costs by 27-fold (from US$7·87 million to $287 000) and 29-fold (from $1·98 million to $69 100) for a system able to detect a SARS-CoV-2-like pathogen before reaching 0·01% cumulative incidence. INTERPRETATION: The large variation in viral relative abundance after controlling for epidemiological factors indicates that other sources of inter-study variation, such as differences in sewershed hydrology and laboratory protocols, have a substantial impact on the sensitivity and cost of W-MGS. Well chosen hybridisation capture panels can greatly increase sensitivity and reduce cost for viruses in the panel, but might reduce sensitivity to unknown or unexpected pathogens. FUNDING: The Wellcome Trust, Open Philanthropy, and Musk Foundation.

Humans↗
PubMed1990

A statistical model for the "N-of-1" study.

The controlled clinical trial has largely replaced case-reports as the authoritative source of information concerning the efficacy of treatment. However, many situations arise in clinical practice where treatment decisions cannot be made on the basis of such studies. The definitive clinical trial may not have been performed, or the results from a particular study may not be applicable to a particular patient. Recently, "N-of-1" studies have been proposed for the experimental evaluation of therapy in a single patient. Multiple courses of active and placebo treatments are administered, and efficacy is determined by following the response measure over a period of time. The purpose of this paper is to present a statistical model appropriate for data arising from this design. The model provides for serial correlation among the response measures captured from the subject, and for heteroskedasticity across the treatment periods. ML estimation procedures are considered, and their properties are investigated. A scoring algorithm is described to iterate to the solution of the ML equations, and considerations for hypothesis testing are presented. The techniques are illustrated through an example.

Aged↗
PubMed1990

A statistical model of the VA/Q distribution.

A "blocks model" is proposed to model the distribution of the ventilation-perfusion ratio (VA/Q distribution). This model is developed from statistical principles and enables the estimated VA/Q distribution to be interpreted in a straightforward and intuitive manner. Estimation of parameters of the blocks model uses a constrained weighted least-squares procedure. Although developed initially to estimate VA/Q distributions from data generated by the multiple inert gas elimination technique (P. D. Wagner, H. A. Saltzman, and J. B. West, J. Appl. Physiol. 36: 588-599, 1974), the blocks method is applicable to any problem in which the unknown distribution is related to the data through an ill-posed integral equation and is particularly suited for problems in which the data are scarce. The method is illustrated with several examples--hypothetical data representing a wide range of VA/Q distributions as well as some real data.

Computer Simulation↗
PubMed1975

A test of several parametic statistical models for estimating success rate in the treatment of carcinoma cervix uteri.

The parametric statistical models discussed include all those which have previously been described in the literature (Boag, 1948-lognormal; Berkson and Gage, 1952-negative exponential; Haybittle, 1959-extrapolated actuarial) and the basic data used to test the models comprised some 3000 case histories of patients treated between 1945 and 1962. The histories were followed up during the period treated between 1945 and 1962. The histories were followed up during the period 1969-71 and thus provided adequate information to validate long-term survival fractions predicted using short-term follow-up data. The results with the log-normal model showed that for series of staged carcinoma cervix patients treated during a 5-year period, satisfactory estimates of long-term survival fractions could be predicted after a minimum waiting period of 3 years for stages I and II, and 2 years for stage III. The model should be used with a value assumed for the lognormal paramater S in the range S = 0.35 to S = 0.40. Although alternative models often gave adequate predictions, the lognormal proved to be the most consistent model. This model may therefore now be used with more confidence for prospective studies on carcinoma cervix series and can provide good estimates of long-term survival fractions several years earlier than would otherwise be possible.

Female↗
PubMed1990

Statistical models for data from periodontal research.

Many factors have been hypothesised either to characterise groups and individuals at risk for periodontal disease or to be markers of periodontal breakdown. In order to identify these as associated either with disease status or progression, a statistical association between the factor and a measure of disease will have to be demonstrated. The statistical modelling of data arising from periodontal research presents special problems. These include the large number of measurements made in each subject, the large magnitude of measurement error compared to the changes in attachment level, the analysis of longitudinal studies, the lack of a measure of instantaneous rate of attachment loss and controversies over the nature of the progression of the disease. We consider statistical methods currently available in the light of these difficulties and identify areas in which further research is necessary.

Analysis of Variance↗
PubMed1992

Multivariate statistical modeling: alternative approach to test evaluation, applied to counting reticulocytes by flow cytometry.

We present a statistical path analysis model for the evaluation of two tests in the absence of a "gold standard" method. This model is applied to the evaluation of flow-cytometric and visual reticulocyte counting by using as the comparison method a combination of three hematological measurements: hemoglobin concentration (HGB), mean cellular volume (MCV), and erythrocyte density width (EDW). We assumed that, in general, a higher reticulocyte count is associated with a lower HGB value and with greater values for MCV and EDW. Applying this assumption and the statistical model, we demonstrated that flow cytometry was superior to visual reticulocyte counting in the low-value range studied. The path analysis model is potentially applicable in other cases where two tests are to be compared, and when no gold standard is available.

Erythrocyte Count↗
PubMed1978

A statistical model for predicting response of breast cancer patients to cytotoxic chemotherapy.

A binary logistic model is used for predicting response to cytotoxic chemotherapy for a breast cancer patient on the basis of her tumor enzyme activity profile. The enzymes used in the model are lactate dehydrogenase, nicotinamide adenine dinucleotide phosphate-isocitrate dehydrogenase, and phosphoglucomutase, all of which were measured on primary tumor specimens from each patient. The statistical model provides an estimate of the probability that an individual will respond to treatment. Chemotherapeutic treatment consisting of combination cytotoxic drugs and subsequent evaluation of patient response followed cooperative group protocol guidelines, including outside review to confirm the patient evaluation. The model based on this study, which represents 5 years of patient follow-up, correctly predicts clinical outcome in 32 of the 37 cases available.

Antineoplastic Agents↗
PubMed1977

Statistical models for renal micropuncture studies.

Statistical issues relating to data analysis of re-collection micropuncture experiments are presented. In the presence of significant animal-treatment interaction, namely, differential response of each animal at different levels of the treatment, the conventional paired or unpaired t testing would not be entirely appropriate. Accordingly, two analysis of variance (ANOVA) models have been derived for the appropriate paired and unpaired designs of micropuncture experiments. Interactive computer programs have been written for both these analyses, and the results are illustrated with experimental data. An example is presented in which the results are statistically significant with paired t testing and by analysis of variance for unequal number of tubules but not when the animal-treatment interaction is included in the analysis of variance model. To investigate linkage in renal transport mechanisms, we propose the use of partial correlation analysis. Experimental results from our laboratory are used to illustrate these techniques.

Analysis of Variance↗
PubMed1991

Computer graphics representation of a statistical model used with computer-aided diagnosis.

A description of computer graphics of a multidimensional model that is used with computer-aided diagnosis or prognosis is presented. The model is discussed and computer graphics of the model are developed. The computer graphics are suitable as visual supplements for presenting the computer-aided diagnostic model to individuals who may be inexperienced in multivariate statistics.

Animals↗
PubMed1979

Statistical models of the demand for emergency medical services in an urban area.

First- and second-order statistical regression models are presented for the Emergency Medical Services (EMS) demand in an urban area as it relates to various socioeconomic, demographic, and other characteristics of the area. Individual models are formulated for different types of medical emergencies with the city of Atlanta, GA, serving as the data base. These models are generally shown to provide excellent fits to the empirical data.

Emergency Medical Services↗