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Results for “Statistics, Nonparametric”

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At least 109 records · Page 6Linked to original sources

PubMed2005

Intraocular pressure control following phacoemulsification in patients with chronic angle closure glaucoma.

OBJECTIVES: To evaluate intraocular pressure (IOP) and glaucoma control following phacoemulsification with posterior chamber intraocular lens implantation in patients who had chronic angle closure glaucoma (CACG) whose peripheral anterior synechiae (PAS) were less than 270 degrees. DESIGN: Non-randomized consecutive cases series. PARTICIPANTS: CACG cases at the glaucoma service, Ramathibodi Hospital who underwent Neodymium YAG laser peripheral iridotomy (PI) and subsequently received or did not receive anti-glaucoma medication. MATERIAL AND METHOD: Retrospective analysis of CACG patients who had PAS 270 degrees or less and underwent YAG-PI with or without anti-glaucoma medication to control IOP at 21 mmHg or less. The IOP and number of anti-glaucoma medication used at 1, 3 and 6 months were measured. Patients were classified into 2 Groups according to degree of PAS: Group 1 were patients who had PAS 180 degrees or less and Group 2 were those whose PAS was between 181 degrees and 270 degrees. MAIN OUTCOME MEASURES: The IOP and number of anti-glaucoma medication at baseline and postoperatively at 1, 3 and 6 months were compared by nonparametric statistics. RESULTS: There were 28 patients (48 eyes) in the present study. Twenty two were females and 6 were males. Patients' age ranged from 45 to 76 years old with a mean of 55 +/- 6.5 years. Of the 48 eyes, 34 were in Group 1 and 14 were in Group 2. In Group 1, the mean baseline IOP was 20 +/- 2.5 mmHg. and the average number of preoperative anti-glaucoma medication used was 0.08. At 1, 3 and 6 months postoperatively, the IOPs were 16.2 +/- 2.2, 17.1 +/- 2.0, 18.1 +/- 1.4 mmHg. respectively with an average number of anti-glaucoma medications of 0, 0.3 and 0.3, respectively, whereas in Group 2, the mean baseline IOP was 22 +/- 3.8 mmHg and mean preoperative number of anti-glaucoma was 1.8, whereas postoperatively, the IOPs at 1, 3 and 6 months were 17.1 +/- 2.2, 17.3 +/- 1.8, and 17.1 +/- 1.7 mmHg, with an average number of 1.1, 1.4 and 1.4 anti-glaucoma medications used, respectively. When compared between the 2 Groups, Group 1 had a significant difference in IOP control at 1 and 3 months and less use of antiglaucoma medications than Group 2 up to at least 6 months. CONCLUSION: Phacoemulsification in CACG helped control of glaucoma. There was a statistically significant difference in IOP reduction and number of anti-glaucoma medication used before and after phacoemulsification in the CACG patients whose PAS did not exceed 270 degrees at least up to 6 months.

Aged↗

PubMed2006

Effects of local serotonin administration on pain and microcirculation in the human masseter muscle.

AIMS: To investigate whether exogenously administered 5-hydroxytryptamine (5-HT) at high or low concentration influences pain and microcirculation in the human masseter muscle. METHODS: In 12 healthy female subjects, 5-HT in 2 concentrations (0.1 micromol/L and 1,000 micromol/L) and isotonic saline were injected into the masseter muscles in a randomized and balanced double-blind manner. The pain intensity after injections was recorded with Borg's rating scale, and intramuscular blood flow was monitored continuously during the experiment with a laser-Doppler technique. Nonparametric statistics were used for analyses. RESULTS: Administration of 5-HT at 1,000 micromol/L induced significantly more pain than saline (Wilcoxon: P < .05), while there was no difference between 5-HT at 0.1 micromol/L and saline. The blood flow did not change significantly after injection of 5-HT at either concentration compared to saline. However, changes in pain intensity and blood flow were positively correlated after injection of 5-HT at 1,000 micromol/L (Spearman: P < .05). CONCLUSION: Intramuscular administration of 5-HT at 1,000 micromol/L into the human masseter muscle induced pain, but 5-HT did not have any effect on local blood flow at either concentration.

Analysis of Variance↗

PubMedDate not supplied

The temporomandibular joint in juvenile rheumatoid arthritis: I. Computed tomographic findings.

The temporomandibular joints (TMJ) of children afflicted with juvenile rheumatoid arthritis (JRA) were evaluated with clinical examinations and computed tomography (CT). Thirty-seven consecutive patients (6-17 years old) from the Texas Scottish Rite Hospital arthritis clinic were studied to investigate morphological abnormalities in the TMJ by CT. Both qualitative and quantitative measures of TMJ morphology were made from axial CT scans. Ten children without JRA served as a control group. Various ANOVA and nonparametric statistical models were used for analysis. Evidence of TMJ abnormalities from the CTs was found in 62% of these JRA children. The TMJ pathosis indices for left and right joints were significantly higher in the JRA subjects than those in the control children (P < 0.03) and joint spaces were narrower (P < 0.02). These features are indicative of TMJ destruction. Thus, there is considerable risk for TMJ involvement and its debilitating and deforming sequelae in children afflicted with JRA.

Adolescent↗

PubMedDate not supplied

The temporomandibular joint in juvenile rheumatoid arthritis: Part II. Relationship between computed tomographic and clinical findings.

A study was undertaken to examine the relationship between the clinical signs and symptoms of temporomandibular joint (TMJ) disorder and computed tomographic (CT) evidence of destruction of these joints in children afflicted with juvenile rheumatoid arthritis (JRA). A thorough clinical examination including determination of the craniomandibular index (CMI) was performed on each of 37 consecutive JRA patients (6-17 years old), who had also received comprehensive evaluations of TMJ morphology by axial CT (see Part I, Pediatr Dent, 17:46-53, 1995). Measures of facial asymmetry (photographic) and mandibular size (cephalometric) also were collected. Published norms for mandibular dimensions and for prevalences of symptoms and signs of TMJ disorders served as control data. Various ANOVA and nonparametric statistical models were used for analysis. Average maximal opening was significantly less in the JRA subjects compared with the controls, and more than 50% of the JRA children manifested chin deviations or vertical disparities between mandibular angle regions, indicating compromised mandibular function and form. With the exception of facial asymmetry, however, none of the clinical signs or symptoms of TMJ dysfunction were remarkable predictors of bony destruction of the TMJ. Subjects with definitive evidence (CT) of TMJ destruction (62%) could not be identified reliably by any of the clinical measures used here. These findings indicate that clinical examination alone is inadequate for detecting condylar degeneration in the TMJ of children with JRA.

Adolescent↗

PubMed1997

[Changes in the size of the stomach and its sections in human early postnatal ontogeny].

The present study represents findings of the examination of change dynamics in dimensions of human stomach and its regions since birth up to the age of 6 months, carried out in cadavers of 40 children using methods of parametric and nonparametric statistics (newborns, below 2 months of age, 2-4 and 4-6 months) according to the results of relative and absolute dimensions of measurements. Differences in parameter growth for anatomical regions of stomach were found. Heterochronous pattern of the stomach (cardial and pyloric) regions increase were found together with the presence of 2 (2 and 4-6 months) periods of intensive growth and the period of the delayed growth (2-4 months).

Aging↗

PubMed1997

GP fundholding and prescribing in UK general practice: evidence from two rural, English Family Health Services Authorities.

BACKGROUND: Two separate prescribing budget regimes (part of GP fundholding and the indicative prescribing scheme) were introduced into UK general practice in April 1991 in an attempt to contain the growth in NHS expenditure on prescribed drugs. OBJECTIVES: The aims of this study are (i) to examine whether the fundholding scheme has been more effective at containing prescribing cost growth than the indicative prescribing scheme and (ii) to ascertain whether its implementation, at a practice level, has been affected by local circumstances and conditions. METHODS: Prescribing cost data were collected from two rural, English Family Health Services Authorities for the financial years 1990/1991 to 1993/1994. Exploratory analysis was performed using regression analysis and nonparametric statistical techniques. RESULTS AND CONCLUSIONS: Initially, the fundholding scheme has been the more effective at containing expenditure on prescribed drugs. However, the implementation of the schemes in rural areas has probably been affected by the existence of practices with permission to dispense drugs to their own patients, due to a lack of pharmacies in such areas.

Aged↗

PubMed2006

Nonparametric trend statistic incorporating dispersion differences in sib pair linkage for quantitative traits.

The Haseman-Elston (HE) regression method and its extensions are widely used in genetic studies for detecting linkage to quantitative trait loci (QTL) using sib pairs. The principle underlying the simple HE regression method is that the similarity in phenotypes between two siblings increases as they share an increasing number of alleles identical by descent (IBD) from their parents at a particular marker locus. In such a procedure, similarity was identified with the locations, that is, means of groups of sib pairs sharing 0, 1, and 2 alleles IBD. A more powerful, rank-based nonparametric test to detect increasing similarity in sib pairs is presented by combining univariate trend statistics not only of locations, but also of dispersions of the squared phenotypic differences of two siblings for three groups. This trend test does not rely on distributional assumptions, and is applicable to the skewed or leptokurtic phenotypic distributions, in addition to normal or near normal phenotypic distributions. The performances of nonparametric trend statistics, including nonparametric regression slope, are compared with the HE regression methods as genetic linkage strategies.

Computer Simulation↗

PubMed2005

MRI tissue classification with neighborhood statistics: a nonparametric, entropy-minimizing approach.

We introduce a novel approach for magnetic resonance image (MRI) brain tissue classification by learning image neighborhood statistics from noisy input data using nonparametric density estimation. The method models images as random fields and relies on minimizing an entropy-based metric defined on high dimensional probability density functions. Combined with an atlas-based initialization, it is completely automatic. Experiments on real and simulated data demonstrate the advantages of the method in comparison to other approaches.

Algorithms↗

PubMed2001

Using weighted Kaplan-Meier statistics in nonparametric comparisons of paired censored survival outcomes.

This research introduces methods for nonparametric testing of weighted integrated survival differences in the context of paired censored survival designs. The current work extends work done by Pepe and Fleming (1989, Biometrics 45, 497-507), which considered similar test statistics directed toward independent treatment group comparisons. An asymptotic closed-form distribution of the proposed family of tests is presented, along with variance estimates constructed under null and alternative hypotheses using nonparametric maximum likelihood estimates of the closed-form quantities. The described method allows for additional information from individuals with no corresponding matched pair member to be incorporated into the test statistic in sampling scenarios where singletons are not prone to selection bias. Simulations presented over a range of potential dependence in the paired censored survival data demonstrate substantial power gains associated with taking into account the dependence structure. Consequences of ignoring the paired nature of the data include overly conservative tests in terms of power and size. In fact, simulation results using tests for independent samples in the presence of positive correlation consistently undershot both size and power targets that would have been attained in the absence of correlation. This additional worrisome effect on operating characteristics highlights the need for accounting for dependence in this popular family of tests.

Humans↗

PubMed1992

Circulating interleukin-1 beta and tumor necrosis factor-alpha concentrations after burn injury in humans.

OBJECTIVES: To measure plasma interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF alpha) concentrations after burn injury and to determine if these concentrations relate to clinical status. DESIGN: Prospective assessment. SETTING: Hospital burn unit. PATIENTS: Thirty-one patients with second- or third-degree burns, covering 10% to 95% of body surface area. MEASUREMENTS AND MAIN RESULTS: Initial concentrations of IL-1 beta were increased (mean 188 +/- 31 pg/mL), and the concentrations for each patient correlated with body temperature at the time of the blood sample (rho = 0.51, p < .015) (rho is a nonparametric statistical measure; a nonparametric analysis is mandatory for data that is categorical [Acute Physiology and Chronic Health Evaluation, APACHE, scores] and data that are not normally distributed [IL-1 beta and tumor necrosis factor, TNF, data]). Mean TNF alpha concentrations were initially 264 +/- 132 pg/mL, and these concentrations were positively related to body temperature (rho = 0.41, p < .05) and inversely related to the total WBC count (rho = -0.45, p < .025). Through the course of hospitalization, plasma cytokine levels fluctuated, but transient increases (sometimes into the nanogram/mL range) did not consistently correspond to changes in clinical signs or severity of illness, as determined by APACHE II scores. The maximum plasma cytokine levels in any patient were not related to age, but maximum IL-1 beta concentrations were inversely related to burn size (rho = -0.46, p < .015). The final IL-1 beta concentrations measured in the patients who died (n = 7) were significantly less than measurements in surviving patients matched for burn size and age taken at approximately the same time after admission. CONCLUSIONS: These results indicate that early after burn injury there is a correspondence of IL-1 beta and TNF alpha with certain host responses, but these correlations disappear with the progression of illness. In general, IL-1 beta and TNF alpha appear to be poor indicators of prognosis during burn injury; however, the association of mortality with low circulating IL-1 beta values supports the concept of IL-1 beta as being an essential mediator of host defenses.

Adolescent↗

PubMed2004

Partly nonparametric approach for determining the limit of detection.

BACKGROUND: According to recent International Organization for Standardization (ISO) standards, the limit of detection (LoD) of an assay should be estimated taking both type I (alpha) and II (beta) errors into account. The suggested procedure, however, supposes gaussian distributions of both blank and sample measurements and a linear calibration curve. In clinical chemistry, asymmetric, nongaussian blank distributions are common, and the calibration curve may be nonlinear. We present a partly nonparametric procedure that takes these aspects into account. METHODS: Using theoretical distribution models and simulation studies, we developed a LoD estimation procedure suitable for the field of clinical chemistry that is partly based on nonparametric statistics. RESULTS: For sample size n, the nonparametrically determined 95th percentile of the blank measurements obtained as the value of the [n(95/100) + 0.5]th ordered observation defines the limit for results significantly exceeding zero [limit of blank (LoB)]. The LoD is the lowest value that is likely to yield a result exceeding the LoB. LoD is estimated as: LoB + cbeta x SDS, where SDS is the analytical SD of a sample with a low concentration; cbeta = z(1 - beta)/[1 - 1/(4 x f)]; z(1 - beta) is the standard normal deviate; and f is the number of degrees of freedom for estimation of SD(S). c(beta) is approximately equal to 1.65 for a type II error of 5%. Approaches and needed tabular values for calculation of confidence limits are presented as well as sample size. Worked examples are given to illustrate estimation and verification of the limit of detection. Simulation results are used to document performance. CONCLUSION: The proposed procedure appears useful for application in the field of clinical chemistry and promotes a standardized approach for estimating LoDs of clinical chemistry assays.

Calibration↗

PubMed2005

Using weighted permutation scores to detect differential gene expression with microarray data.

A class of nonparametric statistical methods, including a nonparametric empirical Bayes (EB) method, the Significance Analysis of Microarrays (SAM) and the mixture model method (MMM) have been proposed to detect differential gene expression for replicated microarray experiments. They all depend on constructing a test statistic, for example, a t-statistic, and then using permutation to draw inferences. However, due to special features of microarray data, using standard permutation scores may not estimate the null distribution of the test statistic well, leading to possibly too conservative inferences. We propose a new method of constructing weighted permutation scores to overcome the problem: posterior probabilities of having no differential expression from the EB method are used as weights for genes to better estimate the null distribution of the test statistic. We also propose a weighted method to estimate the false discovery rate (FDR) using the posterior probabilities. Using simulated data and real data for time-course microarray experiments, we show the improved performance of the proposed methods when implemented in MMM, EB and SAM.

Algorithms↗

PubMed2003

Quantitation and comparison of anti-Gal-alpha-1,3-Gal antibodies in sera of healthy individuals and patients waiting for kidney transplantation.

Highly sensitized patients have poor prospects of being offered an allogeneic donor transplant, therefore, they could become primary candidates for xenogeneic organ transplantation. Hyperacute rejection is initiated by anti-Gal-(alpha)-1,3-Gal antibodies (xenoAb) and this rejection will have to be avoided if xenotransplantation is introduced into clinical practice. Hence, the aim of the study was to determine if sensitized patients against HLA antigens have higher titers of xenoAb than nonsensitized individuals. We determined immunoglobulin (Ig)M and IgG xenoAb in the serum of 100 volunteer blood donors and 98 sensitized patients and compared antibody titers from nonsensitized individuals to those with HLA specific antibodies classified into 5 panel-reactive antibody (PRA) groups: I, 0%; II, >0% and < or =10%; III, >10% and < or =50%; IV, >50% and < or =80%; and V, >80%. Analysis of the isotype specific quantification of the xenoAb revealed great interindividual variation but there were no significant differences in the range of titers of xenoAb. No significant PRA group-related variations were observed for xenoAb. In fact, there was no demonstrable correlation between levels of PRA and levels of xenoAb because the scattergram showed no statistically significant association by nonparametric statistic analysis. The results presented herein revealed that the presence of HLA specific antibody has no demonstrable relationship to the presence of higher titers of xenoAb. Thus, sensitized patients do not present a greater risk of rejection or are more difficult to treat for natural xenoreactivity than nonsensitized patients.

Antibodies↗

PubMed2004

[Differences in cerebral glucose metabolism between frontotemporal lobar degeneration and Alzheimer's disease].

OBJECTIVE: To describe differences in cerebral glucose metabolism between frontotemporal lobar degeneration (FTLD) and Alzheimer's disease (AD). METHODS: 14 patients with FTLD (7 f/7 m, mean age 60.1 years) and 14 patients with AD (7 f/7 m, mean age 59.5 years) were examined. [18F]FDG positron emission tomography (PET) scans were analysed with statistical nonparametric mapping (SnPM) and statistical parametric mapping (SPM99). RESULTS: Significant decreases in glucose metabolism in FTLD compared to AD were detected in the left insula/left inferior frontal gyrus (Brodman area [BA]13, 45 and 47) and in the medial frontal gyrus bilaterally (BA10). A significant decrease in AD compared to FTLD was identified in the right middle temporal gyrus (BA39). CONCLUSION: Cerebral PET could be a promising tool to discriminate FTLD from AD.

Aged↗

PubMed2002

Vitamin A levels and immunity in humans.

In animal studies, vitamin A deficiency induces a shift from type 2 (humoral) to type 1 (cellular) cytokines; there are no similar data for humans. Control of human immunodeficiency virus (HIV) and Mycobacterium tuberculosis infections requires type 1 cytokine (cellular) immunity. These infections and vitamin A deficiency are highly prevalent in Africa. We therefore examined the interactions among serum vitamin A levels, immune parameters, HIV infection status, Mycobacterium bovis BCG vaccine scarring (as an indicator of a type 1 cytokine profile), and clinical findings for 70 hospitalized children in Malawi, Africa. Directly conjugated monoclonal antibodies and flow cytometry were used to assess cell-specific cytokine production by peripheral blood monocytes and lymphocyte subpopulations. The statistical techniques employed included nonparametric statistics and logistic regression analyses. Thirty percent of the participants had severe vitamin A deficiency (<10 microg/dl), 34% had moderate deficiency (10 to <20 microg/dl), and 36% had normal levels (> or = 20 microg/dl). Vitamin A levels were lower for HIV-positive than for HIV-negative children (median, 10 and 17 microg/dl, respectively). Vitamin A-deficient children (<20 microg/dl) were more likely than non-vitamin A-deficient children to have higher proportions of natural killer (NK) cells (median, 8.3 and 5.2%, respectively) and lower ratios of interleukin-10-producing monocytes to tumor necrosis factor alpha-producing monocytes after induction (median, 1.0 and 2.3, respectively). Vitamin A-deficient children were also more likely than non-vitamin A-deficient children to exhibit respiratory symptoms (47% versus 12%) and visible BCG vaccine scars (83% versus 48%), which are indicative of a type 1 response to vaccination. Vitamin A status did not vary with gender, age, incidence of malaria parasitemia, blood culture positivity, or rates of mortality (6% of vitamin A-deficient children died versus 20% of non-vitamin A-deficient children). Lower vitamin A levels were associated with a relative type 1 cytokine dominance and proportionately more NK cells, both of which may be somewhat beneficial to persons who are exposed to HIV, M. tuberculosis, or other type 1 pathogens.

BCG Vaccine↗

PubMedDate not supplied

Effect of lumbar orthotics on trunk muscle strength.

Weakening of the trunk muscles is thought to be one disadvantage of prolonged lumbar orthotic use. This study examines weakness of the trunk flexor and extensor muscles in patients who are wearing lumbar orthotics for extended periods. Strength of the trunk flexor and trunk extensor muscles was tested in 24 individuals, using the Kinetic computer. Both concentric and eccentric forces were recorded. Four groups of patients were studied. Group 1 (n = 6) consisted of patients with low back pain who had used a lumbar orthotic for a prolonged period of time. Group 2 (n = 6) consisted of hospital employees with no history of low back pain, who wore lumbar orthotics prophylactically, for back protection. Group 1C (n = 6) consisted of healthy controls, with no history of either back pain or lumbar orthotic use, who were individually age- and gender-matched to each patient in Group 1. Group 2C (n = 6) consisted of healthy controls matched in the same fashion to each patient in Group 2. After consultation with a statistician, statistical analysis was performed using the Wilcoxon's test. Nonparametric statistics were chosen because of the lack of evidence of a normal distribution of the parameters being studied. This analysis revealed significant weakness in concentric flexion (P = 0.0464), concentric extension (P = 0.0277), and eccentric extension (P = 0.0464) in Group 1 compared with matched controls in Group 1C. The only significant weakness compared with controls in Group 2 was in eccentric flexion (P = 0.0277). Trends were toward weakness in the orthotic users for the other motions studied, with a P value of less than 0.1 for eccentric extension. Prolonged use of lumbar orthotics may be associated with trunk muscle weakness in the population studied. Prescribers should continue to limit duration of use when possible and to consider strengthening exercises when prolonged use is anticipated.

Adult↗

PubMed1996

Nonparametric simulation-based statistics for detecting linkage in general pedigrees.

We present here four nonparametric statistics for linkage analysis that test whether pairs of affected relatives share marker alleles more often than expected. These statistics are based on simulating the null distribution of a given statistic conditional on the unaffecteds' marker genotypes. Each statistic uses a different measure of marker sharing: the SimAPM statistic uses the simulation-based affected-pedigree-member measure based on identity-by-state (IBS) sharing. The SimKIN (kinship) measure is 1.0 for identity-by-descent (IBD) sharing, 0.0 for no IBD status sharing, and the kinship coefficient when the IBD status is ambiguous. The simulation-based IBD (SimIBD) statistic uses a recursive algorithm to determine the probability of two affecteds sharing a specific allele IBD. The SimISO statistic is identical to SimIBD, except that it also measures marker similarity between unaffected pairs. We evaluated our statistics on data simulated under different two-locus disease models, comparing our results to those obtained with several other nonparametric statistics. Use of IBD information produces dramatic increases in power over the SimAPM method, which uses only IBS information. The power of our best statistic in most cases meets or exceeds the power of the other nonparametric statistics. Furthermore, our statistics perform comparisons between all affected relative pairs within general pedigrees and are not restricted to sib pairs or nuclear families.

Algorithms↗

PubMed1991

Statistical analysis of categorical data.

This article has presented the most widely used techniques for analyzing categorical data. Data that are qualitative are naturally categorical. Even continuous (or measurement) data can be classified into categories (eg, ages can be grouped into above and below 40) and, hence, these procedures can be applied to a wide range of data. All of these statistical tests are classified as nonparametric statistics, although many statistical textbooks treat hypothesis testing of categorical data separately from the more common nonparametric methods. The most widely used nonparametric procedures will be reviewed in the next issue.

Data Interpretation, Statistical↗