Two questions arising in the analysis of functional magnetic resonance imaging (fMRI) data acquired during periodic sensory stimulation are: i) how to measure the experimentally determined effect in fMRI time series; and ii) how to decide whether an apparent effect is significant. Our approach is first to fit a time series regression model, including sine and cosine terms at the (fundamental) frequency of experimental stimulation, by pseudogeneralized least squares (PGLS) at each pixel of an image. Sinusoidal modeling takes account of locally variable hemodynamic delay and dispersion, and PGLS fitting corrects for residual or endogenous autocorrelation in fMRI time series, to yield best unbiased estimates of the amplitudes of the sine and cosine terms at fundamental frequency; from these parameters the authors derive estimates of experimentally determined power and its standard error. Randomization testing is then used to create inferential brain activation maps (BAMs) of pixels significantly activated by the experimental stimulus. The methods are illustrated by application to data acquired from normal human subjects during periodic visual and auditory stimulation.

Statistical methods of estimation and inference for functional MR image analysis

S-Plus is a powerful environment for statistical and graphical analysis of data. It provides the tools to implement many statistical ideas which have been made possible by the widespread availability of workstations having good graphics and computational capabilities. This book is a guide to using S-Plus to perform statistical analyses and provides both an introduction to the use of S-Plus and a course in modern statistical methods. All data sets and S-Plus functions used are supplied with the book on a diskette.

Modern applied statistics with S-Plus

A method is developed that caters for the application of correspondence analysis to two-way contingency tables with one and two ordered sets of categories. The method involves calculating orthogonal polynomials of the type described by EMERSON (1968), and partitioning the chi-square statistic using the method described in LANCASTER (1953). The method has all the features of simple correspondence analysis, although allows for additional information about the structure and association of the data to be made by isolating location, dispersion and higher order components of the rows and columns.

Simple Correspondence Analysis of Ordinal Cross‐Classifications Using Orthogonal Polynomials

We did a series of observational studies and manipulative experiments on the guild of nocturnal visitors of Agave macroacantha, including (1) a description of the hourly patterns of visits by moths and bats, (2) an evaluation of the relative contribution of bats and moths to flowering success, and (3) an evaluation of the pollination efficiency of the different bat species. Scapes exposed to moths but excluded to bats yielded ∼50% fewer fruits than those exposed to both pollinator groups. Flowers exposed to the bat species Leptonycteris curasoae showed similar fruiting success to those exposed to Choeronycteris mexicana and to those exposed to the whole nocturnal visitor guild. However, the fruits originated from flowers pollinated by Leptonycteris curasoae yielded significantly more seed than those exposed to Choeronycteris mexicana or to the whole pollinator guild. It is concluded that Agave macroacantha is extremely dependent on nocturnal pollinators for its reproductive success and that bats are especially important for successful pollination. Some of these pollinators are migratory and have been reported to be steadily declining. A continuing decline in the populations of pollinators may impede the successful sexual reproduction of the plant host and may put the long-term survival of this agave species under risk.

Pollination ecology of Agave macroacantha (Agavaceae) in a Mexican tropical desert. II. The role of pollinators.

In a study of sexual reproduction in long-lived semelparous plants, we observed Agave macroacantha in the tropical desert of Tehuacan-Cuicatlan, Mexico, describing duration of flowering, flower phenology, and nectar production patterns. We also performed two manipulative experiments evaluating (a) the seed production efficiency of different crossing systems (selfing, cross-pollination, apomixis, and control), and (b) the effect of different pollinators (diurnal exposure to pollinators, nocturnal exposure, exclusion, and control) on the seeds produced. Flowering occurred from early May to late July and had a mean duration of 29 days in the individual rosettes. The flowers were protandrous; anthesis occurred in the afternoon of the third day after floral opening, and the pistils matured in the afternoon of the fifth day. The stigmas remained receptive from dusk to the following morning. Pollination was mostly allogamous. Nectar was produced principally during the night, from the first stages of floral aperture until the stigmas wilted and flowering ceased. The flowers were visited during the day by hymenoptera, butterflies, and hummingbirds and during the night by bats and moths. Only the nocturnal visitors, however, were successful pollinators. Agave macroacantha is extremely dependent on nocturnal pollinators for its reproductive success.

Pollination ecology of Agave macroacantha (Agavaceae) in a Mexican tropical desert. I. Floral biology and pollination mechanisms

l. A Brief Introductory Guide to S-PLUS. 2. Chapter 1-Data Description and Simple Inference: IQ Scores Of Children of De-pressed and Non-Depressed Women. 3. Chapter 2-Multiple Regression: Predicting the Volume of Black Cherry Trees from Measurements of their Height and Diameter. 4. Chapter 3-Analysis of Variance: Diets for Chickens. 5. Chapter 4-Logistic Regression: Predicting Outcome of Treatment for Patients with Leukemia. 6. Chapter 5-Survival Analysis: Modelling the Survival Times of Patients with Leukemia. 7. Chapter 6-Non-Linear Modelling: Fitting the Michaelis-Menten Equation to Hormone-Receptor Assay Results. 8. Chapter 7-The Analysis of Time Series: Yearly Numbers of Sunspots. 9. Chapter 8-Principal Components:Exploring the Progress of Competitors in a 100 Kilometer Road Race. 10. Chapter 9-Cluster Analysis: Classifying Countries in Terms of the Athletic Prowess of their Women. ll. Chapter 10-Correspondence Analysis: Suicide Behaviour in the Former West Germany. 12. Chapter 11-Scattergrams and Density Estimation: Birth and Death Rates for 69 Countries.

A Handbook of Statistical Analyses Using S-Plus.

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A Handbook of Statistical Analyses Using S-Plus.