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PubMed2004

Do associations between airborne particles and daily mortality in Mexico City differ by measurement method, region, or modeling strategy?

We evaluated whether associations between PM10 and daily mortality in Mexico City differ by the PM10 measurement device or by regional differences in particle composition. Additionally, we reanalyzed previously collected data in light of recent insights about flaws in commonly used time series analysis techniques. We examined daily associations between mortality and four indicators of ambient PM10 using Poisson regression, controlling for temperature and time trends with cubic natural splines. Associations were calculated for five subregions corresponding to five monitoring sites and pooled for the entire metropolitan area. PM10 was measured with three methods: Tapered Element Oscillating Microbalance (TEOM), Sierra-Anderson High Volume (Hi-Vol) and Harvard Impactor (HI), the latter only at one site. In addition, predicted values of daily PM10 were developed using the Hi-Vol measurements, which were taken every sixth day, and weather, visibility and other pollutant data. We assigned deaths to the exposure from the monitor nearest to their residence. We also re-evaluated the HI PM2.5 and mortality association in southwest Mexico City, which was estimated previously using nonparametric statistical models. Slight decreases in effect estimates were observed (a 1.45% increase (95% CI: 0.09%, 2.83%) in total mortality per 10 microg/m(3) increment of PM2.5 at lag 0) compared to a 1.68% change (95% CI: 0.45%, 2.93%) using the previously employed nonparametric approach. Using data pooled over all the regions, PM10 measured by the TEOM and the predicted PM10 values showed little association with mortality at any of the lags examined. The pooled estimates for Hi-Vol PM10 (using one sixth of the data) were positive across all lags examined and significant for lags 3 and 5. No consistent patterns of differing associations were seen across regions that would correspond with particle toxicity or composition. Particulate air pollution, measured with gravimetric methods, is associated with daily mortality and presents a risk to health in Mexico City. The reanalysis suggests that previous research is robust to statistical method and likely to yield the same overall conclusions about the short-term effects of airborne particles on mortality.

Air Pollutants↗

PubMed1980

Interpretation of research data: selected statistical procedures.

Selected statistical procedures used in the analysis of research data are presented. The relationship of significance testing to research hypotheses is explained in terms of tests of differences and correlation. Also, the differences, assumptions, and advantages and disadvantages of parametric and nonparametric statistics are discussed. With regard to each statistic presented, emphasis is placed on the hypotheses that would be tested, the kinds of data for which the statistic is appropriate, the method of calculation, and how to test for "significance." The selected statistical procedures include the Student's t-test and chi square. An explanation of the concept of correlation is provided, and several correlation coefficients are discussed, including the Pearson r, Spearman rho, Kendall's tau, the point biserial, biserial, phi coefficient, and contingency coefficient. Pharmacists must know basic statistical procedures in order to be able to effectively interpret the results of published research or to appropriately analyze data that have been collected in their own research endeavors.

Methods↗

PubMed1984

The effect of light sleep on the brainstem auditory evoked potential (BAEP).

This study dealt with the latency and amplitude changes in the brainstem auditory evoked potential (BAEP) measured during periods from wake to light sleep, after stimulating both ears of 16 subjects. All 13 latencies (positive and negative) increased from the central vertex electrode (referred C7 vertebra) with statistical significance from peak VI (and II), and 8 of 13 latencies increased from the (ipsilateral) ear electrode with statistical significance from negative peak V. Furthermore, a significant decrease in amplitude occurred in peak V (ear) and in peak VIII (Cz and ear). Finally, the more typical recording of vertex to ipsilateral ear showed all 13 latencies increasing in the sleep state and nonparametric statistics showed significance in 6 of these latencies. The assumption that the latencies and amplitudes do not change from the waking to the sleeping state should be reconsidered.

Brain Stem↗

PubMed1983

Evaluation of alaryngeal voice quality by nonparametric procedures.

Alaryngeal voice quality was evaluated based on nonparametric statistics. Twenty voice samples of the vowel /e/ were recorded from sixteen alaryngeal and four normal speakers, and were randomized and presented to twenty normal listeners. The listeners rated the voices using seven-point scales consisting of twelve pairs of polar-opposite adjectives. By means of nonparametric procedures such as the Wilcoxon signed rank test, significant differences in the rating scores were detected for certain combinations of the voice samples, the classes of voicing methods, the listeners and the rating scales. Quality of the alaryngeal voices differed significantly from that of the normal voices on some of the rating scales. The results suggest the nonparametric procedures are useful to evaluate alaryngeal voice quality.

Adult↗

PubMed1980

On transforming biological data to Gaussian form.

Much of the statistical analysis of biological data depends on the assumption that the data are Gaussian (or normal). Some well-known procedures which use this assumption are (i) t-tests (ii) analysis of variance (iii) regression estimation and their attendant tests. If the data are not Gaussian, one can use nonparametric statistical techniques, if they exist, but they often require larger amounts of data to obtain equally precise results (see for example Lumsden and Mullen (7) for a discussion of this with regard to reference value estimation). If the data are not Gaussian a fruitful approach to their analyses lies in trying to find a transformation which will render tham Gaussian. The data thus transformed to a Gaussian form, can be analyzed validly using standard statistical techniques. The process of finding a good transformation of the data has often been an arbitrary and ad hoc one. The purpose of this article is to look at a particular technique for attempting to render nonGaussian data Gaussian, and to illustrate its applicability and breadth of use.

Animals↗

PubMed1984

Irradiation-hyperthermia in canine hemangiopericytomas: large-animal model for therapeutic response.

Results of irradiation-hyperthermia treatment in 11 dogs with naturally occurring hemangiopericytoma were reported. Similarities of canine and human hemangiopericytomas were described. Orthovoltage X-irradiation followed by microwave-induced hyperthermia resulted in a 91% objective response rate. A statistical procedure was given to evaluate quantitatively the clinical behavior of locally invasive, nonmetastatic tumors in dogs that were undergoing therapy for control of local disease. The procedure used a small sample size and demonstrated distribution of the data on a scaled response as well as transformation of the data through classical parametric and nonparametric statistical methods. These statistical methods set confidence limits on the population mean and placed tolerance limits on a population percentage. Application of the statistical methods to human and animal clinical trials was apparent.

Animals↗

PubMed1996

The critical period for surgical treatment of dense congenital unilateral cataract.

PURPOSE: Early treatment of dense congenital unilateral cataract is associated with better acuity outcomes. It is unclear whether there is a gradual worsening of prognosis with delay of treatment from the time of birth (linear model) or whether there exists an early window of time during which treatment is maximally effective, followed by declining success (bilinear model). The aim of the current study was to determine which model better describes the response to treatment. METHODS: A maximum likelihood procedure that permits statistical comparison between linear and bilinear models was applied to acuity outcomes from a group of 45 children 5 to 8 years of age with a history of dense congenital unilateral cataract diagnosed at 1 to 10 days of age. Contrast sensitivity and vernier acuity data from a subset of these children were evaluated with nonparametric statistical methods. RESULTS: The bilinear model provided a significantly better fit to the acuity outcome data. The line fitted to the initial portion of the function had a shallow slope that was not significantly different from 0.0. The intersection of the two linear functions occurred at 5.6 weeks and was followed by a steep decline in visual acuity outcomes. Contrast sensitivity and vernier outcome measures over a range of spatiotemporal conditions showed better outcomes were obtained with early treatment. CONCLUSIONS: Intervention before 6 weeks of age may minimize the effects of congenital unilateral deprivation on the developing visual system and provide for optimal rehabilitation of visual acuity.

Aphakia, Postcataract↗

PubMed2004

Increasing the power and efficiency of disease-marker case-control association studies through use of allele-sharing information.

Case-control disease-marker association studies are often used in the search for variants that predispose to complex diseases. One approach to increasing the power of these studies is to enrich the case sample for individuals likely to be affected because of genetic factors. In this article, we compare three case-selection strategies that use allele-sharing information with the standard strategy that selects a single individual from each family at random. In affected sibship samples, we show that, by carefully selecting sibships and/or individuals on the basis of allele sharing, we can increase the frequency of disease-associated alleles in the case sample. When these cases are compared with unrelated controls, the difference in the frequency of the disease-associated allele is therefore also increased. We find that, by choosing the affected sib who shows the most evidence for pairwise allele sharing with the other affected sibs in families, the test statistic is increased by >20%, on average, for additive models with modest genotype relative risks. In addition, we find that the per-genotype information associated with the allele sharing-based strategies is increased compared with that associated with random selection of a sib for genotyping. Even though we select sibs on the basis of a nonparametric statistic, the additional gain for selection based on the unknown underlying mode of inheritance is minimal. We show that these properties hold even when the power to detect linkage to a region in the entire sample is negligible. This approach can be extended to more-general pedigree structures and quantitative traits.

Alleles↗

PubMed1978

An analysis of phytohemagglutinin lymphoblastogenesis in whole blood.

A population of 80 defined normal people ranging in age from 20 to 62 years were used to define a dose response curve in whole blood phytohemagglutinin blastogenesis of lymphocytes. Maximum stimulation occurred at four days of incubation and 18 hours of pulse labeling with tritiated thymidine using 50 micrograms per milliliter of phytohemagglutinin and 1 microcurie of tritiated thymidine. An analysis of variants indicates a statistically significant trend of reduction of disintegrations per minute per milliliter with advancing age. Likewise, there was an extremely significant difference between measurements performed in the morning and late in the afternoon. Measurements referred to sex and sequential testing were not shown to be significant. Therefore, whole blood phytohemagglutinin blastogenesis may be meaningfully performed and interpreted using nonparametric statistics and the raw blastogenesis of a standard amount of peripheral whole blood, provided that the remainder of the test conditions are rigidly controlled.

Adult↗

PubMedDate not supplied

A pilot study for the statistical treatment of nutritional parameters in the quality control of canned fishing goods.

This pilot study was derived as a consequence of European Directives 496/90 and 493/91 in which a regulation on the labeling of canned fishing goods was established. The study was intended primarily to assess whether different Spanish canned fishing goods might be differentiated by their basic nutritional composition (i.e., ash, chlorine as NaCl, fat, humidity, total proteins, and dry residue) and, second, to study each particular type of good. Accordingly, a univariate nonparametric statistical test and 2 multivariate chemometric techniques (factor and cluster analyses) were used. The pilot study revealed that (1) the basic nutritional variables did not allow a clear distinction among canned goods when different commodities were considered, but they seemed useful for obtaining information for only one type of good; and (2) the variables that gave the most useful information to visualize the appearance of groups in the data sets were humidity, dry residue, fat, and proteins, although their particular usefulness was found to be different when different species were considered.

Animals↗

PubMed1992

Measuring the quality of life of patients with benign prostatic hyperplasia. Assessment of the usefulness of a new quality of life questionnaire specially adapted to benign prostatic hyperplasia patients.

A questionnaire consisting of 36 questions based on a visual analogue scale for measuring the quality of life (QOL) of benign prostatic hyperplasia (BPH) patients is presented and assessed. The sensitivity of the questionnaire is demonstrated by its ability to register a statistically significant (p less than 0.01) improvement of QOL after prostate surgery (transurethral resection of the prostate). Its reliability is shown by its ability to give reproducible results in a nonoperated BPH patient group. Patient compliance has been excellent. It is discussed to what extent questions directly concerning symptoms from prostatism should be included in QOL questionnaires for BPH patients. Nonparametric statistics are applied. It is concluded that questionnaires like this are useful tools in the assessment of BPH patients, irrespective of the treatment modality. They will probably be of particular value in studies of drug therapy of BPH, complementing methods of assessment like symptom score and urodynamic parameters.

Humans↗

PubMed1992

A simple computer program with statistical tests for the analysis of enzyme kinetics.

A simple computer program that calculates the kinetic parameters of enzyme reactions is described. Parameters are determined by nonlinear, least-squares regression using either Marquardt-Levenberg or Gauss-Newton algorithms to find the minimum sum of squares. Three types of enzyme reactions can be analyzed: single substrate reactions (Michaelis-Menten and sigmoidal kinetics), enzyme activation at a fixed substrate value or enzyme inhibition at a fixed substrate value. The user can monitor goodness of fit through nonparametric statistical tests (performed automatically by the computer) and through visual examination of the pattern of residuals. The program is unique in providing equations for activator and inhibition analysis as well as in enabling the user to fix some of the parameters before regression analysis. The simplicity of the program makes it extremely useful for quickly determining kinetic parameters during the data-gathering process.

Biometry↗

PubMed2000

Evidence for a strong sulfur-aromatic interaction derived from crystallographic data.

We have uncovered new evidence for a significant interaction between divalent sulfur atoms and aromatic rings. Our study involves a statistical analysis of interatomic distances and other geometric descriptors derived from entries in the Cambridge Crystallographic Database (F. H. Allen and O. Kennard, Chem. Design Auto. News, 1993, Vol. 8, pp. 1 and 31-37). A set of descriptors was defined sufficient in number and type so as to elucidate completely the preferred geometry of interaction between six-membered aromatic carbon rings and divalent sulfurs for all crystal structures of nonmetal-bearing organic compounds present in the database. In order to test statistical significance, analogous probability distributions for the interaction of the moiety X-CH(2)-X with aromatic rings were computed, and taken a priori to correspond to the null hypothesis of no significant interaction. Tests of significance were carried our pairwise between probability distributions of sulfur-aromatic interaction descriptors and their CH(2)-aromatic analogues using the Smirnov-Kolmogorov nonparametric test (W. W. Daniel, Applied Nonparametric Statistics, Houghton-Mifflin: Boston, New York, 1978, pp. 276-286), and in all cases significance at the 99% confidence level or better was observed. Local maxima of the probability distributions were used to define a preferred geometry of interaction between the divalent sulfur moiety and the aromatic ring. Molecular mechanics studies were performed in an effort to better understand the physical basis of the interaction. This study confirms observations based on statistics of interaction of amino acids in protein crystal structures (R. S. Morgan, C. E. Tatsch, R. H. Gushard, J. M. McAdon, and P. K. Warme, International Journal of Peptide Protein Research, 1978, Vol. 11, pp. 209-217; R. S. Morgan and J. M. McAdon, International Journal of Peptide Protein Research, 1980, Vol. 15, pp. 177-180; K. S. C. Reid, P. F. Lindley, and J. M. Thornton, FEBS Letters, 1985, Vol. 190, pp. 209-213), as well as studies involving molecular mechanics (G. Nemethy and H. A. Scheraga, Biochemistry and Biophysics Research Communications, 1981, Vol. 98, pp. 482-487) and quantum chemical calculations (B. V. Cheney, M. W. Schulz, and J. Cheney, Biochimica Biophysica Acta, 1989, Vol. 996, pp.116-124; J. Pranata, Bioorganic Chemistry, 1997, Vol. 25, pp. 213-219)-all of which point to the possible importance of the sulfur-aromatic interaction. However, the preferred geometry of the interaction, as determined from our analysis of the small-molecule crystal data, differs significantly from that found by other approaches.

Crystallography, X-Ray↗

PubMedDate not supplied

Cyclandelate versus propranolol in the prophylaxis of migraine--a double-blind placebo-controlled study.

The aim of the present study was to ascertain the comparative efficacy of cyclandelate, a migraine prophylactic with calcium overload blocking properties, versus propranolol, a non-selective beta-adrenergic blocker, and placebo. Based on different statistical analysis procedures (including time series analysis) a responder and nonresponder evaluation for cyclandelate and propranolol was performed. In addition, an attempt was made to identify the dose relationship of the various drugs on headache parameters. In a double-blind placebo-controlled study 84 patients were treated in a placebo run-in phase (4 weeks). The patients were then randomized by the statistical criterion of placebo responder and nonresponder to either the cyclandelate or the propranolol group. The total treatment period included a low-dosage phase (8 weeks) and high-dosage phase (8 weeks). All patients kept a headache diary before, during and after treatment. The data were assessed by time series analysis (ARIMA), as well as by analysis of variance and nonparametric statistics. Based on ARIMA statistics, 39.3% of the patients showed a significant improvement of migraine during treatment with cyclandelate compared with 29.4% placed on propranolol. Higher doses of cyclandelate and propranolol were more effective. Using the qualitative response-criterion of a 50% reduction in migraine symptoms, cyclandelate showed a response in 67.9% and propranolol in 41.2% of all cases. It can therefore be concluded that cyclandelate as well as propranolol are two comparable substances in the prophylactic treatment of migraine, with cyclandelate showing fewer side effects.

Adolescent↗

PubMed1996

Evaluation of pedicle screw insertion monitored by intraoperative evoked electromyography.

The insertion of pedicle screws monitored by evoked electromyography (EMG) was prospectively evaluated in the 132 consecutive patients. The technique involved constant-voltage stimulation and was statistically evaluated at both the arbitrary 20- and 40-V settings. The patients were postoperatively evaluated clinically and radiographically. Computed tomography (CT) scanning was performed for new neurologic deficits. Results were divided into three groups: type 1, a negative EMG response; type 2, a positive EMG response, but no corrective action taken; and type 3, a positive EMG response and corrective action undertaken. Nonparametric statistics were used to evaluate the results at both the 20- and 40-V settings. In the type 3 group, in which corrective action was undertaken, there were no neurologic injuries or screw removals, a statistically significant result. Looking at the two intensity levels, at 20- and 40-V settings, there were no statistically significant differences in the three classifications at either intensity level. We concluded the evoked EMG for monitoring pedicle screw insertion is an efficacious adjunct. A positive response at < 20 V with the constant-voltage technique warrants corrective action.

Adult↗

PubMed1987

Renal pelvic carcinoma: morphological correlates of metastatic behavior.

We report a clinicopathological analysis of morphological parameters in relation to subsequent biological behavior in 48 patients with renal pelvic carcinoma. The relationships of subsequent metastasis to tumor stage and grade, as well as the presence of vascular, renal parenchymal or renal hilar invasion were evaluated by parametric and nonparametric statistical tests. Corrected 5-year survival rates for grades 1 to 3 tumors were 100, 67 and 5 per cent, respectively. Grade 3 tumors demonstrated more invasion of the blood vessels, hilus and renal parenchyma compared to grades 1 and 2 tumors (p less than 0.005, 46 patients). Moreover, invasion of renal hilar tissues had greater predictive value for subsequent distant metastatic spread (95 per cent, nonparametric) than either vascular (83 per cent) or renal parenchymal (77 per cent) invasion. Metastases developed in 27 of 48 patients during followup periods of 2 to 39 years. The pattern of metastatic lesions revealed that local spread to hilar soft tissues occurred in 92 per cent of the patients who subsequently had distant metastases. Spread to retroperitoneal lymph nodes and ipsilateral ureteral mucosa occurred in 84 and 44 per cent of the patients, respectively. Our study illustrates the potential value of analysis of individual histological parameters to evaluate the likelihood of subsequent metastasis.

Aged↗

PubMed1979

Statistical analysis of method comparison data. Testing normality.

A Lilliefors test of normality has been applied to data from precision and accuracy studies. Most data sets tested as non-normal. Simulation studies showed that the test is extremely sensitive to the rounded, narrowly distributed data that are typical of method performance studies in clinical chemistry. The Lilliefors test can be modified to be applicable to rounded data so that it gives fewer indications of non-normality. The authors conclude that the selection of a test of normality requires careful study of the properties of the test. Otherwise, the subsequent choice between parametric and nonparametric statistics may not be meaningful.

Chemistry, Clinical↗

PubMed1998

Technical note: the initial stages of statistical data analysis.

OBJECTIVE: To provide an overview of several important data-related considerations in the design stage of a research project and to review the levels of measurement and their relationship to the statistical technique chosen for the data analysis. BACKGROUND: When planning a study, the researcher must clearly define the research problem and narrow it down to specific, testable questions. The next steps are to identify the variables in the study, decide how to group and treat subjects, and determine how to measure, and the underlying level of measurement of, the dependent variables. Then the appropriate statistical technique can be selected for data analysis. DESCRIPTION: The four levels of measurement in increasing complexity are nominal, ordinal, interval, and ratio. Nominal data are categorical or "count" data, and the numbers are treated as labels. Ordinal data can be ranked in a meaningful order by magnitude. Interval data possess the characteristics of ordinal data and also have equal distances between levels. Ratio data have a natural zero point. Nominal and ordinal data are analyzed with nonparametric statistical techniques and interval and ratio data with parametric statistical techniques. ADVANTAGES: Understanding the four levels of measurement and when it is appropriate to use each is important in determining which statistical technique to use when analyzing data.

Journal Article↗