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Two methods of statistical inference for EEG pattern discrimination are described with examples of their application. One concerns whether an arbitrary EEG pattern belongs to a standard EEG group or not, and the other concerns whether a group of EEG belongs to the standard EEG group.
Concentrations of prolactin in plasma were measured in 176 dairy cows and heifers from 13 days before calving to 2.5 days after calving over 21 mo. Prolactin averaged 35.1, 115.0, and 34.4 ng/ml prepartum (days -13 to -2), peripartum (days -1.0 to +.5), and postpartum (days +1.5 and +2.5). Season of the year affected prolactin in all periods. The linear covariate of daily photoperiod (hours of daylight per 24 h) accounted for as much variation in prolactin prepartum and postpartum as did linear covariates of both photoperiod and average daily temperature. However, it was possible to account for additional seasonal variation in prolactin peripartum by addition of the temperature covariate to the photoperiod covariate. Although photoperiod was related either directly or indirectly more than temperature to factors affecting prolactin seasonally, these statistical inferences cannot prove that prolactin is more dependent on photoperiod than on temperature because the two metereorological measures were correlated (r = .84). When the data were grouped for correlation analysis by months, correlations between temperature and prolactin among prepartum samples collected in the spring and in the fall were positive, small but significant.
A procedure of sire evaluation for multiple binary responses when information is missing for some traits is described. The genetic model assumes a conceptual underlying multivariate normal distribution rendered discrete by abrupt thresholds. Statistical inferences are made from a posterior distribution consisting of several conditionally independent likelihood functions and a multivariate normal prior distribution. Each likelihood function corresponds to a particular class of information available. Point estimators and predictors of fixed and random effects are the values that maximize the posterior distribution conditionally on heritabilities and genetic correlations. The procedure involves nonlinear maximization. An example involving joint selection for calving ease and skeletal development illustrates the principles. Application of the methodology as a potential means of removing bias due to selection for categorical traits is discussed.
OBJECTIVE: The goal of this study was to investigate the safety and tolerability of the novel endothelin A (ETA) receptor antagonist clazosentan in patients with subarachnoid hemorrhage (SAH) and its potential to reduce the incidence and severity of cerebral vasospasm following surgical clipping of the aneurysm. METHODS: This Phase IIa multicenter study had two parts: a double-blind, randomized Part A (some patients given clazosentan [0.2 mg/kg/hr] and others given placebo), in which statistical inference was performed, and an open-label Part B (patients with established vasospasm given clazosentan [0.4 mg/kg/hr for 12 hours followed by 0.2 mg/kg/hr]) for exploratory purposes only. Primary end points were the incidence and severity of angiographic vasospasm on Day 8 after SAH and the safety and tolerability of the drug. Thirty-four patients (Hunt and Hess Grades III and IV and Fisher Grade > or = 3) were recruited and 32 (15 in the clazosentan group and 17 in the placebo group) were retained in the intent-to-treat population; 19 patients entered Part B. In Part A, treatment with clazosentan resulted in a reduced incidence of angiographically evident cerebral vasospasm (40% compared with 88% of patients, p = 0.008). In addition, the severity of vasospasm was reduced in the clazosentan group (p = 0.012). In Part B of the study, in 50% of assessable patients who were initially treated with placebo reversal of vasospasm was observed following the initiation of clazosentan therapy. The incidence of new infarctions was 15% in the clazosentan group and 44% in the placebo group (p = 0.130). There was no adverse event pattern indicating a specific organ toxicity of clazosentan. CONCLUSIONS: This study indicates that clazosentan reduces the frequency and severity of cerebral vasospasm following severe aneurysmal SAH with the incidence and severity of adverse events comparable to that of placebo.
A systems framework was used to study the unusual failure rate on the National Council Licensing Examination (NCLEX) experienced by one-third of the 1983 graduates of a Northwestern Bachelor of Science Nursing (BSN) program. The study group included 176 graduates; 28 were nonsuccessful and 148 were successful candidates. All candidates experienced an integrated curriculum in the two-year nursing major. This comprehensive study addressed the conceptual and experiential areas of the curriculum as well as student academic potential and performance. It is one of the first research reports to include the new NCLEX as the dependent variable. Data were analyzed for correlational and causal relationships using regression analysis and tests of statistical inference. Results indicated that graduates who entered the program with low SAT scores, low cumulative and Science GPAs, who scored below the class mean on School of Nursing examinations and whose cumulative grade point averages drifted downward while in the School of Nursing were at a significantly high risk of failing the NCLEX. It was demonstrated that the bulk of the learners attracted to the University program fell in the B to C range of academic performance, some graduates were dissatisfied with faculty teaching skill and methods, as well as with the amount of hands-on experience available either in skills labs or clinical settings. The integrated curriculum used by the School of Nursing, threading concepts across practice areas, also presented a difficulty for students. Overall, the study indicated a concern about whether the avant-garde integrated curriculum and teaching methods used by the School of Nursing met the needs of average learners attracted to the program.
The attenuation performance of a hearing protector is used to estimate the protected exposure level of the user. The aim is to reduce the exposed level to an acceptable value. Users should expect the attenuation to fall within a reasonable range of values around a norm. However, an analysis of extensive test data indicates that there is a negative relationship between attenuation performance and the standard deviation. This result is deduced using a variation in the method of calculating a single number rating of attenuation that is more amenable to drawing statistical inferences. As performance is typically specified as a function of the mean attenuation minus one or two standard deviations from the mean to ensure that greater than 50% of the wearer population are well protected, the implication of increasing standard deviation with decreasing attenuation found in this study means that a significant number of users are, in fact, experiencing over-protection. These users may be disinclined to use their hearing protectors because of an increased feeling of acoustic isolation. This problem is exacerbated in areas with lower noise levels.
OBJECTIVES: To assess Web-based waiting time information services to identify how they aimed to meet the information needs of patients and general practitioners, and to evaluate how well waiting time information was presented. DESIGN: A cross-sectional survey of six government websites in English-speaking countries with publicly funded hospitals. Sites were evaluated on the clarity of instructions about how their information should be used, and the accuracy of the statistics they contained was assessed indirectly using methodological criteria. RESULTS: The services were judged to encourage GPs and patients to use the statistics to avoid surgical units with long waiting times, but overall advice was poor. Services did not state whether the statistics predicted expected waiting times, and just one stated that the statistics were only intended as a guide. Statistics were based on different types of data, and derived at different levels of aggregation, raising questions of accuracy. Most sites explained waiting list terms, but provided inadequate advice on the uncertainty associated with making statistical inferences. CONCLUSIONS: GPs and patients should use Web-based waiting time information services cautiously because of a lack of guidance on how to appropriately interpret the presented information.
BACKGROUND: CAG repeat expansions in ATXN2 are implicated as risk factors for several neurological diseases, including spinocerebellar ataxia type 2 (SCA2) when >=33 CAG repeats are present, and amyotrophic lateral sclerosis (ALS) when 27-33 CAG repeats are present. However, how haplotypes around the repeats and CAA interruptions within the repeats are associated with disease phenotypes remains poorly understood. Previous studies on haplotypes around ATXN2 were limited to SNPs very close to the repeats (<5kb) or were based on statistical inference only. METHODS: Here, we used long-read sequencing on the Oxford Nanopore Technologies (ONT) platform to simultaneously infer haplotypes around ATXN2, the number of CAG repeats, and the number of CAA interruptions, along with NYGC ALS Consortium NGS dataset. We further sequenced 41 individuals (EUR = 39) with neurological diseases with intermediate repeats by ONT. RESULTS: We found that haplotypes around ATXN2 and the number of interruptions show ethnicity-specific and ALS-specific distribution. Three CAA interruptions are present at low prevalence (~1%) in control populations in multiple ancestry groups, but high prevalence (~55%) in ALS individuals with intermediate repeats. Furthermore, we examined 159 individuals with ALS (~90% European ancestry) with intermediate ATXN2 repeats and found a unique haplotype in ALS individuals with three CAA interruptions, which can be tagged by an SNV, rs148019457. We also validated that the rs148019457-G allele is only present in haplotypes with three CAA interruptions. CONCLUSIONS: In summary, our study shows that 3 CAA interruptions are rarely seen in healthy controls but are common in those with expanded ATXN2 CAG repeats who have neurological disorders, and that rs148019457 tags a specific haplotype with 3 CAA interruptions within expanded ATXN2 CAG repeats in individuals of European ancestry. These results have implications for the development of precision genomic medicine for neurological disorders, and the tag SNP may help identify those with interruptions from existing population genotyping data.
BACKGROUND: We exemplify the use of a marginal approach with proportional hazards model when failure times are correlated. METHODS: The marginal distribution for each failure time is formulated by the Cox proportional hazards model, while the dependence structure is unspecified. However, a correct variance-covariance estimate of the regression coefficients that takes into account the intra-group correlation is proposed. The program MULCOX2 which implements this statistical methodology is used to assess the effect of a nutritional supplementation intervention on pressure ulcer development on critically ill older patients from a multicentric trial (involving 19 wards). We compare the results obtained with those of the usual Cox regression. RESULTS: The naive approach yields much smaller standard error estimates of the regression parameters than the robust approach. CONCLUSION: In our example, the results obtained with the marginal approach do not modify the conclusions: a nutritional supplementation intervention tends to decrease significantly the formation of pressure ulcers. However in other situations, ignoring the intra-cluster dependence could lead to invalid statistical inference. The variability of the estimated effects by MULCOX2 can be quite sensitive to the number of clusters in the sample and to the clusters size.
AIM: From a personal experience of 23 treated gastrointestinal stromal tumor (GISTs), this study analyzed both clinical and diagnostic problems of this quite new nosological category. MATERIALS AND METHODS: A this literature review provides a rigid selection of papers (scientific basis, statistic inference, type/quality of the journal, etc.); only numerous series have been included (case reports were excluded) and only those published after 1990. Three-hundred-seventy-five cases have therefore been selected. Starting and late symptoms/signs and diagnostic tests employed were analyzed. RESULTS: Results show 1) a relevant GIST quantity (approx. 30%) is casually discovered, during operations carried out for other pathologies or diagnostic tests for other indications; 2) poor correlation between site of the tumor and clinical manifestations; 3) a positive correlation between tumor diameter and presence of symptoms/signs seems to exists. The accuracy of different diagnostic tests is reported. CONCLUSION: No specific symptoms/signs have been isolated; this kind of tumor is often accidentally found. An analysis of different diagnostic tests available today shows the very important role of endoscopic ultra-sound, together with CT and MRI.
Because psychological assessment typically lacks biological gold standards, it traditionally has relied on clinicians' expert knowledge. A more empirically based approach frequently has applied linear models to data to derive meaningful constructs and appropriate measures. Statistical inferences are then used to assess the generality of the findings. This article introduces artificial neural networks (ANNs), flexible nonlinear modeling techniques that test a model's generality by applying its estimates against "future" data. ANNs have potential for overcoming some shortcomings of linear models. The basics of ANNs and their applications to psychological assessment are reviewed. Two examples of clinical decision making are described in which an ANN is compared with linear models, and the complexity of the network performance is examined. Issues salient to psychological assessment are addressed.
In positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) data sets, the number of variables is larger than the number of observations. This fact makes application of multivariate linear model analysis difficult, except if a reduction of the data matrix dimension is performed prior to the analysis. The reduced data set, however, will in general not be normally distributed and therefore, the usual multivariate tests will not be necessarily applicable. This problem has not been adequately discussed in the literature concerning multivariate linear analysis of brain imaging data. No theoretical foundation has been given to support that the null distributions of the tests are as claimed. Our study addresses this issue by introducing a method of constructing test statistics that follow the same distributions as when the data matrix is normally distributed. The method is based on the invariance of certain tests over a large class of distributions of the data matrix. This implies that the method is very general and can be applied for different reductions of the data matrix. As an illustration we apply a test statistic constructed by the method now presented to test a multivariate hypothesis on a PET data set. The test rejects the null hypothesis of no significant differences in measured brain activity between two conditions. The effect responsible for the rejection of the hypothesis is characterized using canonical variate analysis (CVA) and compared with the result obtained by using univariate regression analysis for each voxel and statistical inference based on size of activations. The results obtained from CVA and the univariate method are similar.
OBJECTIVE: This paper aims at describing the behavior of tobacco's demand in Mexico across four one-year periods: 1992, 1994, 1996, and 1998, as well as to estimate a cigarette demand function. MATERIAL AND METHODS: A cross-sectional study with longitudinal analysis was conducted. Information sources were the Encuesta Nacional de Ingreso y Gasto de los Hogares (ENIGH) (National Survey of Household Income and Spending) (NHSIS) and the tobacco pack prices reported by the Procuraduría Federal del Consumidor (Profeco) (Federal Office of Consumer's Protection) (FOCP). Spending, income, and prices were deflated to 1994 prices; the population was stratified into quintiles of real income, by rural and urban areas. Indicators of daily consumption of cigarettes and packs were constructed and prices per pack calculated. Adjusted prevalence figures were estimated. Logistic and linear regression models were used for statistical inference; a cigarette demand function was estimated using multivariate logistic regression, to find socioeconomic determinants of cigarette consumption. RESULTS: The adjusted prevalence of household tobacco spending fell from 22.4 to 9.9% between 1992 and 1998. Households allocated more than 4% of their income to tobacco consumption. A trend between income level and cigarette spending was observed, with the first quintile (the poorest population) allocated a greater share of their income than higher quintiles. The average daily consumption of cigarettes increased from 7.5 to 9.8 between 1992 and 1998. It was estimated that 90% of "smoker homes" consumed up to one package per day. The proportion of non-filter cigarettes increased from 0.4 to 4.8% between 1992-1998, with a bigger increase in 1996. Finally, it was found that the most important determinants of spending were prices and income. CONCLUSIONS: Policies focusing on tobacco prices would help to reduce tobacco consumption and improve the health of the Mexican population.
Reviews of epidemiological studies of cardiovascular effects of occupational noise have been published regularly in the literature. The first part of this paper summarises the conclusions which have been drawn. The second part focuses in more detail on the results of studies in which noise exposure was not assessed by objective measurements, but on the basis of subjective ratings as given by the study subjects in a questionnaire. Finally, the paper addresses some issues of occupational noise studies which deserve special attention from the methodological and conceptual point of view. These are concerned with study design, statistical inference, selection and confounding bias, overcontrolling, effect modification and exposure misclassification.
At the turn of the 20th century, Mendel's laws were found to be applicable to human blood groups. Within two decades, blood group genetics were applied to problems of parentage. Expansion of immunohematology into leukocyte antigen identification produced the single most informative, expressed polymorphism. About the same time, analysis of a great number of soluble protein polymorphisms followed advances in electric separation methods, enzymology, and immunochemistry. As new, independent loci were discovered, the power to exclude the falsely accused increased, and it became possible to apply Bayesian principles to determined probabilities of biologic relationships. The revolution in nucleic acid technology has dramatically improved analysis and statistical inferences. By the turn of the 21st century, laboratories should be able to determine biologic parentage with virtual certainty.
The majority of studies evaluating the efficacy of periodontal therapy have been conducted in university-based clinical trials under ideal and well-controlled conditions, where time (and cost) effectiveness was not an overriding factor. In Australia, where the larger proportion of dental treatment is provided by the private sector, there are no clinical studies which provide information on the efficacy of periodontal treatment in general or specialist private practice. The overall purpose of this study was to evaluate the efficacy of periodontal therapy in a specialist private practice over an initial period of 5.3 years in a group of 100 patients, and subsequently on the remaining 70 patients followed over a period 13.5 years. Hence the total observation period extended over nearly two decades. Using frequency distributions of site data, and statistical inferences based on the patient as the experimental unit, the results indicated an overall improvement and subsequent stability in clinical attachment in all categories of Initial Probing Depths, for both single- and multi-rooted teeth, for teeth treated with root planing alone and those that required adjunctive surgical intervention, and for younger and older patients. It was also noted that very few teeth were lost over the extended observation period. These positive results were achieved in a most favourable time in the initial phase of treatment (1.5-2.0 hours) as compared with the protracted time frame (5-8 hours) recorded in university-based clinical trials. Similarly, professional maintenance therapy took an average of around two appointments per year (1 hour) compared with an average of 3-4 hours per year in the university-based studies. The results therefore proved not only satisfactory from the standpoint of clinical parameters measured but also on the basis of time efficiency.
OBJECTIVE: The objective of this research was to evaluate the level of knowledge about adolescence, pubertal development and sexuality among adolescents from 10 to 14 years old at municipal public schools in Feira de Santana-Bahia, 2000. METHODS: Cross-sectional study, with a randomized and proportional sample out of a population of 6,419 students in the municipal Public System. The level of knowledge was analyzed according to age, sex and educational level. Data was collected by means of a specific confidential questionnaire, which was pre-tested. A scale of values (score--satisfactory, reasonable and unsatisfactory) was established according to the percentage and proportional number of right answers regarding general and specific topics. Statistical inference was calculated by chi-square with a significance of 5% as well as the bivariate and multivariate analysis, calculating the simple and adjusted prevalence, through stratified analysis. RESULTS: Adolescents showed unsatisfactory level of information about terms, particularly those at the age of 10 (69.2%) and 11 years (70.6%), female (61.7%) and the ones in the 4th (82.8%) and 5th (61.1%) grades. The level of knowledge according to sex, adjusted by age and educational level, showed that females are 1.3 and 1.27 times more likely to present an unsatisfactory level of knowledge than males. The level of knowledge according to educational level, adjusted by age, showed that those subjects between 4th and 5th grades are 2.32 times more likely to present an unsatisfactory level of knowledge if compared to students of 6th and 8th grades, with significant differences (p<0.05). CONCLUSIONS: The high prevalence of unsatisfactory level of knowledge with significant association between 4th and 5th grades and females points to the necessity of educative actions regarding health and sexuality in the beginning of adolescence at municipal public schools.
PURPOSE: Protocols for quantifying the surface roughness of implants are varied and dependent upon the roughness parameter produced by the particular measurement device. The objective of this study was to examine the accuracy and precision of typical roughness characterization instruments used in the dental implant industry. MATERIALS AND METHODS: The average roughness (Ra) was measured using 2 common surface characterization instruments: an interferometer and a stylus profilometer. Titanium disks were prepared to represent 4 typical dental implant surfaces: machined, acid-etched, hydroxyapatite-coated, and titanium plasma-sprayed. Repeated measurements from multiple sites on each surface were undertaken to establish statistical inferences. Qualitative images of the surfaces were also acquired using a laser scanning confocal microscope. After surface measurements were conducted, the disks were diametrically cut and cross-sectional profiles were examined using a scanning electron microscope (SEM) as a comparative measure of surface topography. An analysis of variance was applied to isolate the effects of the measurement site, measurement sequence, surface treatment, and instrument type on Ra values. RESULTS: The results indicated that surface treatment (P = .0001) and instrument (P = .0001) strongly influenced Ra data. By design, measurement site (diametrical: P = .9859; area: P = .9824) and measurement sequence (P = .9990) did not influence roughness. In the assessment of individual instrument accuracy, the interferometer was the most accurate in predicting SEM-based roughness (P = .6688) compared with the stylus (P = .0839). As a measure of aggregate precision over all measurements, the most repeatable instrument was the stylus (coefficient of variation [CV] = 0.108), followed by the interferometer (CV = 0.125) and SEM (CV = 0.273). DISCUSSION: These results indicate dependencies in accuracy and precision related to the surface characterization technique. CONCLUSION: Instrument variability may obscure functional correlations between implant surface topography and osseointegration.