Joint Probability (joint + probability)

Distribution by Scientific Domains


Selected Abstracts


Patterns of Vocal Interactions in a Bullfrog (Rana catesbeiana) Chorus: Preferential Responding to Far Neighbors

ETHOLOGY, Issue 8 2000
Su L. Boatright-Horowitz
In chorusing species, males seem to be spaced non-randomly, and their vocal interactions may be governed by particular behavioral rules. We monitored patterns of vocal interactions in a natural bullfrog (Rana catesbeiana) chorus to determine the probability with which calls of individual frogs would follow each other's in dyadic sequences. Expected probabilities of responses in a dyad were calculated based upon the joint probabilities of calling (relative calling rates) of the individual frogs; observed probabilities of response reflected the actual number of following responses in each dyad. Results of statistical tests comparing observed and expected probabilities of responding revealed that, when dyads were closely spaced, observed probabilities of a following response were significantly less than the expected probabilities. Conversely, when dyads were composed of more distant males, observed probabilities of responding were significantly greater than expected. Observed probabilities of response were correlated with inter-male distances; males called more frequently than expected following calls of far neighbors, and less frequently than expected following calls of near neighbors. These data suggest that males attend to both nearby and distant callers, and adjust the onset of their own vocalizations appropriately. Males may be actively inhibited by calls of their near neighbors, and their calling may be actively elicited by the calls of their far neighbors. [source]


What is learned from experience in a probabilistic environment?

JOURNAL OF BEHAVIORAL DECISION MAKING, Issue 3 2004
Stephen E. Edgell
Abstract Three experiments explored what is learned from experience in a probabilistic environment. The task was a simulated medical decision-making task with each patient having one of two test results and one of two diseases. The test result was highly predictive of the disease for all participants. The base rate of the test result was varied between participants to produce different inverse conditional probabilities of the test result given the disease across conditions. Participants trained using feedback to predict a patient's disease from a test result showed the classic confusion of the inverse error, substituting the forward conditional probability for the inverse conditional probability when tested on it. Additional training on the base rate of the test result did little to improve performance. Training on the joint probabilities, however, produced good performance on either conditional probability. The pattern of results demonstrated that experience with the environment is not always sufficient for good performance. That natural sampling leads to good performance was not supported. Further, because participants not trained on joint probabilities did, however, know them but still committed the confusion of the inverse error, the hypothesis that having joint probabilities would facilitate performance was not supported. The pattern of results supported the conclusion that people learn all the necessary information from experience in a probabilistic environment, but depending upon what the experience was, it may interfere with their ability to recall to memory the appropriate sample set necessary for estimating or using the inverse conditional probability. Copyright © 2004 John Wiley & Sons, Ltd. [source]


A semi-Markov model for binary longitudinal responses subject to misclassification

THE CANADIAN JOURNAL OF STATISTICS, Issue 3 2001
Rhonda J. Rosychuk
Abstract The authors propose a two-state continuous-time semi-Markov model for an unobservable alternating binary process. Another process is observed at discrete time points that may misclassify the true state of the process of interest. To estimate the model's parameters, the authors propose a minimum Pearson chi-square type estimating approach based on approximated joint probabilities when the true process is in equilibrium. Three consecutive observations are required to have sufficient degrees of freedom to perform estimation. The methodology is demonstrated on parasitic infection data with exponential and gamma sojourn time distributions. Un modèle semi-markovien pour données longitudinales binaires sujettes à des erreurs de classification Les auteures proposent un modèle semi-markovien à temps continu et à deux états pour un processus binaire alternant non-observable. Un processus auxiliaire observé en temps discret renseigne toutefois de façon imparfaite quant à l'état réel du processus d'intér,t. Pour estimer les paramètres du modèle, les auteures proposent la minimisation d'un critère de type khi-deux de Pearson en s'appuyant sur une approximation des probabilités conjointes du processus en équilibre. Trois observations consécutives fournissent suffisamment de degrés de liberté aux fins d'estimation. La méthodologie est illustrée au moyen de données sur une infection parasitaire avec temps de séjour exponentiel et gamma. [source]


Adaptive Randomization for Multiarm Comparative Clinical Trials Based on Joint Efficacy/Toxicity Outcomes

BIOMETRICS, Issue 3 2009
Yuan Ji
Summary We present an outcome-adaptive randomization (AR) scheme for comparative clinical trials in which the primary endpoint is a joint efficacy/toxicity outcome. Under the proposed scheme, the randomization probabilities are unbalanced adaptively in favor of treatments with superior joint outcomes characterized by higher efficacy and lower toxicity. This type of scheme is advantageous from the patients' perspective because on average, more patients are randomized to superior treatments. We extend the approximate Bayesian time-to-event model in Cheung and Thall (2002,,Biometrics,58, 89,97) to model the joint efficacy/toxicity outcomes and perform posterior computation based on a latent variable approach. Consequently, this allows us to incorporate essential information about patients with incomplete follow-up. Based on the computed posterior probabilities, we propose an AR scheme that favors the treatments with larger joint probabilities of efficacy and no toxicity. We illustrate our methodology with a leukemia trial that compares three treatments in terms of their 52-week molecular remission rates and 52-week toxicity rates. [source]


Gallager bounds on the performance of maximum-likelihood decoded linear binary block codes in AWGN interference

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 1 2007
Shahram Yousefi
Performance evaluation of maximum-likelihood (ML) soft-decision-decoded binary block codes is usually carried out using bounding techniques. Many tight upper bounds on the error probability of binary codes are based on the so-called Gallager's first bounding technique (GFBT). In this method, Gallager bisects the error probability to the joint probability of error and noise residing in a region , (here referred to as the Gallager region) plus joint probability of error and noise residing in the complement of , (also referred to as regions of many and few errors, respectively); where , is a volume around the transmitted codeword. In this tutorial review, a comprehensive study of a number of upper bounds on the error probability of ML decoding of binary codes based on GFBT is provided. For some bounds, their applicability to other schemes is also pointed out and argued. We also provide an overview of bounds based on Gallager's second bounding technique (GSBT) and discuss some of their relations and interconnections. Copyright © 2006 AEIT [source]


Developing a post-fire flood chronology and recurrence probability from alluvial stratigraphy in the Buffalo Creek watershed, Colorado, USA,

HYDROLOGICAL PROCESSES, Issue 15 2001
John G. Elliott
Abstract Stratigraphic and geomorphic evidence indicate floods that occur soon after forest fires have been intermittent but common events in many mountainous areas during the past several thousand years. The magnitude and recurrence of these post-fire flood events reflects the joint probability between the recurrence of fires and the recurrence of subsequent rainfall events of varying magnitude and intensity. Following the May 1996 Buffalo Creek, Colorado, forest fire, precipitation amounts and intensities that generated very little surface runoff outside of the burned area resulted in severe hillslope erosion, floods, and streambed sediment entrainment in the rugged, severely burned, 48 km2 area. These floods added sediment to many existing alluvial fans, while simultaneously incising other fans and alluvial deposits. Incision of older fans revealed multiple sequences of fluvially transported sandy gravel that grade upward into charcoal-rich, loamy horizons. We interpret these sequences to represent periods of high sediment transport and aggradation during floods, followed by intervals of quiescence and relative stability in the watershed until a subsequent fire occurred. An alluvial sequence near the mouth of a tributary draining a 0·82 km2 area indicated several previous post-fire flood cycles in the watershed. Dendrochronologic and radiocarbon ages of material in this deposit span approximately 2900 years, and define three aggradational periods. The three general aggradational periods are separated by intervals of approximately nine to ten centuries and reflect a ,millennium-scale' geomorphic response to a closely timed sequence of events: severe and intense, watershed-scale, stand-replacing fires and subsequent rainstorms and flooding. Millennium-scale aggradational units at the study site may have resulted from a scenario in which the initial runoff from the burned watershed transported and deposited large volumes of sediment on downstream alluvial surfaces and tributary fans. Subsequent storm runoff may have produced localized incision and channelization, preventing additional vertical aggradation on the sampled alluvial deposit for several centuries. Two of the millennium-scale aggradational periods at the study site consist of multiple gravel and loam sequences with similar radiocarbon ages. These closely dated sequences may reflect a ,multidecade-scale' geomorphic response to more frequent, but aerially limited and less severe fires, followed by rainstorms of relatively common recurrence. Published in 2001 John Wiley & Sons, Ltd. [source]


On multiple portmanteau tests,

JOURNAL OF TIME SERIES ANALYSIS, Issue 5 2009
Naoya Katayama
Abstract., The portmanteau statistic based on the first m residual autocorrelations is used for diagnostic checks on the adequacy of fitting a model with varying m. In this article, we propose an approximation of the joint probability of multiple portmanteau tests with different degrees of freedom (DF). This distribution is easy to compute when all DF are even integers; its empirical behaviour is clarified in terms of asymptotic theory. [source]


Probability-based protein secondary structure identification using combined NMR chemical-shift data

PROTEIN SCIENCE, Issue 4 2002
Yunjun Wang
Abstract For a long time, NMR chemical shifts have been used to identify protein secondary structures. Currently, this is accomplished through comparing the observed 1H,, 13C,, 13C,, or 13C, chemical shifts with the random coil values. Here, we present a new protocol, which is based on the joint probability of each of the three secondary structural types (,-strand, ,-helix, and random coil) derived from chemical-shift data, to identify the secondary structure. In combination with empirical smooth filters/functions, this protocol shows significant improvements in the accuracy and the confidence of identification. Updated chemical-shift statistics are reported, on the basis of which the reliability of using chemical shift to identify protein secondary structure is evaluated for each nucleus. The reliability varies greatly among the 20 amino acids, but, on average, is in the order of: 13C,>13C,>1H,>13C,>15N>1HN to distinguish an ,-helix from a random coil; and 1H,>13C, >1HN ,13C,,13C,,15N for a ,-strand from a random coil. Amide 15N and 1HN chemical shifts, which are generally excluded from the application, in fact, were found to be helpful in distinguishing a ,-strand from a random coil. In addition, the chemical-shift statistical data are compared with those reported previously, and the results are discussed. A JAVA User Interface program has been developed to make the entire procedure fully automated and is available via http://ccsr3150-p3.stanford.edu. [source]