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PubMed1987

Multiple comparisons and nonparametric statistical tests on a programmable calculator.

Calculator programs are provided for statistical tests for comparing groups of data. These tests can be applied when t-tests are inappropriate, as for multiple comparisons, or for evaluating groups of data that are not distributed normally or have unequal variances. The programs, designed to run on the least expensive Hewlett-Packard programmable scientific calculator, Model HP-11C, should place these statistical tests within easy reach of most students and investigators.

Analysis of Variance↗
PubMed1975

Some nonparametric statistical tests for quick evaluation of clinical data.

Some rapid statistical tests give (a) rapid answers on how well methods agree and control chart evaluation (sign and run tests) and (b) evaluation of distribution of test results (Tukey's quick test and run test). These tests mainly require counting of data and the use of the given nomograms. An unusual distribution of patient test values--that is, unusual when compared with the generally observed distribution of the data seen in a particular laboratory--may indicate laboratory error, alteration of specimens (as from poor collection and/or storage techniques, such as evaporation), or an unusual patient population.

Clinical Laboratory Techniques↗
PubMed2004

Powerful allele sharing statistics for nonparametric linkage analysis.

Nonparametric linkage analysis is widely used to map susceptibility genes for complex diseases. This paper introduces six nonparametric statistics for measuring marker allele sharing among the affected members of a pedigree. We compare the power of these new statistics and three previous statistics to detect linkage with Mendelian diseases having recessive, additive, and dominant modes of inheritance. The nine statistics represent all possible combinations of three different IBD scoring functions and three different schemes for sampling genes among affecteds. Our results strongly suggest that the statistic T(rec)(blocks) is best for recessive traits, while the two statistics T(kin)(pairs) and T(all)(kin) vie for best for an additive trait. The best statistic for a dominant trait is less clear. The statistics T(kin)(pairs) and T(all)(kin) are equally promising for small sibships, but in extended pedigrees the statistics T(dom)(blocks) and T(dom)(pairs) appear best. For a complex trait, we advocate computing several of these statistics.

Alleles↗
PubMed2001

A new nonparametric linkage statistic for mapping both qualitative and quantitative trait loci.

We describe an alternative nonparametric linkage (NPL) statistic to that of Kruglyak et al. [Am. J. Hum. Genet. 58:1347-63, 1996] that can be used with qualitative phenotypes, and is easily extended for use with quantitative phenotypes. We analyzed the Genetic Analysis Workshop 12 simulated isolated population data, replicate 1, using two phenotypes; affected status (AFF) a dichotomous phenotype and quantitative trait Q5, which was chosen since it was the most strongly associated with AFF. One false positive significant NPL score was observed for the AFF phenotype. For Q5 a single region on chromosome 1 reached genome-wide significance. The peak of this signal was for marker D01G137 at 135.1 cM with a quantitative trait locus (QTL)-NPL score of 4.19. The nearest marker to the true location of the major gene (MG5 at 137.1 cM) was D01G139 at position 135.8 cM, where the QTL-NPL score was still high at 4.08.

Chromosome Mapping↗
PubMed2001

A survey of affected-sibship statistics for nonparametric linkage analysis.

We have compared the power of a large number of allele-sharing statistics for "nonparametric" linkage analysis with affected sibships. Our rationale was that there is an extensive literature comparing statistics for sibling pairs but that there has not been much guidance on how to choose statistics for studies that include sibships of various sizes. We concentrated on statistics that can be described as assigning scores to each identity-by-descent-sharing configuration that a pedigree might take on (Whittemore and Halpern 1994). We considered sibships of sizes two through five, 27 different genetic models, and varying recombination fractions between the marker and the trait locus. We tried to identify statistics whose power was robust over a wide variety of models. We found that the statistic that is probably used most often in such studies-S(all)-performs quite well, although it is not necessarily the best. We also found several other statistics (such as the R criterion, S(robdom), and the Sobel-and-Lange statistic C) that perform well in most situations, a few (such as S(-#geno) and the Feingold-and-Siegmund version of S(pairs)) that have high power only in very special situations, and a few (such as S(-#geno), the N criterion, and the Sobel-and-Lange statistic B) that seem to have low power for the majority of the trait models. For the most part, the same statistics performed well for all sibship sizes. We also used our results to give some suggestions regarding how to weight sibships of different sizes, in forming an overall statistic.

Alleles↗
PubMed2001

Statistics for nonparametric linkage analysis of X-linked traits in general pedigrees.

We have compared the power of several allele-sharing statistics for "nonparametric" linkage analysis of X-linked traits in nuclear families and extended pedigrees. Our rationale was that, although several of these statistics have been implemented in popular software packages, there has been no formal evaluation of their relative power. Here, we evaluate the relative performance of five test statistics, including two new test statistics. We considered sibships of sizes two through four, four different extended pedigrees, 15 different genetic models (12 single-locus models and 3 two-locus models), and varying recombination fractions between the marker and the trait locus. We analytically estimated the sample sizes required for 80% power at a significance level of.001 and also used simulation methods to estimate power for a sample size of 10 families. We tried to identify statistics whose power was robust over a wide variety of models, with the idea that such statistics would be particularly useful for detection of X-linked loci associated with complex traits. We found that a commonly used statistic, S(all), generally performed well under various conditions and had close to the optimal sample sizes in most cases but that there were certain cases in which it performed quite poorly. Our two new statistics did not perform any better than those already in the literature. We also note that, under dominant and additive models, regardless of the statistic used, pedigrees with all-female siblings have very little power to detect X-linked loci.

Alleles↗
PubMed1996

Functional magnetic resonance imaging of symptom provocation in obsessive-compulsive disorder.

BACKGROUND: The new technique of functional magnetic resonance imaging was used to investigate the mediating neuroanatomy of obsessive-compulsive disorder symptoms. METHODS: Ten patients with obsessive-compulsive disorder and 5 normal subjects were studied via functional magnetic resonance imaging during control and provoked conditions. Data analysis entailed parametric and nonparametric statistical mapping. RESULTS: Statistical maps (nonparametric; P < 10(-3)) showed activation for 70% or more of patients with obsessive-compulsive disorder in medial orbitofrontal, lateral frontal, anterior temporal, anterior cingulate, and insular cortex, as well as caudate, lenticulate, and amygdala. No normal subjects exhibited activation in any brain region. CONCLUSIONS: Results of functional magnetic resonance imaging were consistent with past studies of obsessive-compulsive disorder that used other functional neuroimaging modalities. However, paralimbic and limbic activations were more prominent in the present study.

Adult↗
PubMed2005

Confidence mapping in diffusion tensor magnetic resonance imaging tractography using a bootstrap approach.

The bootstrap technique is an extremely powerful nonparametric statistical procedure for determining the uncertainty in a given statistic. However, its use in diffusion tensor MRI tractography remains virtually unexplored. This work shows how the bootstrap can be used to assign confidence to results obtained with deterministic tracking algorithms. By invoking the concept of a "tract-propagator," it also underlines the important effect of local fiber architecture or architectural milieu on tracking reproducibility. Finally, the practical advantages and limitations of the technique are discussed. Not only does the bootstrap allow any deterministic tractography algorithm to be used in a probabilistic fashion, but also its model-free inclusion of all sources of variability (including those that cannot be modeled) means that it provides the most realistic approach to probabilistic tractography.

Algorithms↗
PubMed2001

Local fundus response to blue (LED and laser) and infrared (LED and laser) sources.

Light damage research began during the early years of laser light exploration. There is a clear and significant literature that identifies an easily demonstrated retina-pigment epithelium pathology which is associated with short wavelength exposures below 520 nm. Recent interest has expanded because of the growing evidence for a blue light contribution to the retina aging process by way of a poorly understood chemical process(es) that involve circulation, oxidative reactions and the spectral absorption properties of the pigment epithelium. New powerful sources of relatively inexpensive blue energy have become available as a family of light emitting diodes. In this experiment, we examined funduscopic, angiographic and scanning laser tomographic measures of the retinal-pigment epithelium response to LED and laser spectral blue and infrared emissions closely matched in wavelengths and delivered under carefully matched circumstances. Ten retinas in normal young rhesus monkeys were locally exposed to various energy density values at 458 nm (Argon laser) ranging from 5 to 54 J cm(-2). Eight rhesus eyes were exposed to LED irradiation with a peak wavelength of 460 nm ranging from 9 to 62 J cm(-2). Similarly, a matched infrared (IR) laser and IR LED pair were used to expose an additional ten eyes for comparison of the long wavelengths. IR irradiance ranged from 21 to 306 J cm(-2). There was no response to IR exposure in any of the eyes. Blue light exposure results were measured from the color fundus photographs, scanning laser tomographs and early- and late-phase fluorescein angiogram responses at 2 and 30 days after the exposure. Results scores were accumulated for the four measures at the two time periods. The resulting lesion scores when plotted against the exposure in J cm(-2)showed no demonstrable effect at irradiance lower than 10 J cm(-2)and near 100% effectiveness for irradiance greater than 30 J cm(-2). The most sensitive and enduring indicator of change was the late fluorescein angiograms. Nonparametric statistical analysis of the scores from the two samples support the conclusion that there is no difference in the consequences of LED and laser light exposures under these matched conditions.

Analysis of Variance↗