Variation In Occurrence Rate Research Articles

A New Wavelet Method for Identification of Eddies and Assessment of Incidents on Islands of the Eastern Caribbean

Using two dimensional continuous wavelet transforms, a novel method for identification of mesoscale eddies is presented to facilitate extraction of characteristics for area, amplitude, type, and location from maps of sea level anomalies. In comparison with the previously established growing method for eddy identification, it is found that the wavelet method identifies more than twice the number of eddies and is particularly better at resolving small eddies down to the 0.25 degree resolution of the data. Such research into eddy identification and tracking is significant to the assessment of eddies with potential to impact on coastlines of small islands. The method is applied to the identification of eddies on tracks towards islands of the Eastern Caribbean over 23 years. Spatial and temporal variation in rate of occurrence and magnitude is established. For Barbados there is an average of 9 anticyclonic incidents a year with maximum amplitude of typically 0.22 m in the dry seasons and 0.16 m in the wet seasons. Seasonal variation is reversed for the other islands with twice the number of anticyclonic incidents having maximum amplitudes of about 0.20 m annually.

Epidemiology of acute kidney injury in critically ill patients: the multinational AKI-EPI study.

Current reports on acute kidney injury (AKI) in the intensive care unit (ICU) show wide variation in occurrence rate and are limited by study biases such as use of incomplete AKI definition, selected cohorts, or retrospective design. Our aim was to prospectively investigate the occurrence and outcomes of AKI in ICU patients. The Acute Kidney Injury-Epidemiologic Prospective Investigation (AKI-EPI) study was an international cross-sectional study performed in 97 centers on patients during the first week of ICU admission. We measured AKI by Kidney Disease: Improving Global Outcomes (KDIGO) criteria, and outcomes at hospital discharge. A total of 1032 ICU patients out of 1802 [57.3%; 95% confidence interval (CI) 55.0-59.6] had AKI. Increasing AKI severity was associated with hospital mortality when adjusted for other variables; odds ratio of stage 1 = 1.679 (95% CI 0.890-3.169; p = 0.109), stage 2 = 2.945 (95% CI 1.382-6.276; p = 0.005), and stage 3 = 6.884 (95% CI 3.876-12.228; p < 0.001). Risk-adjusted rates of AKI and mortality were similar across the world. Patients developing AKI had worse kidney function at hospital discharge with estimated glomerular filtration rate less than 60 mL/min/1.73 m(2) in 47.7% (95% CI 43.6-51.7) versus 14.8% (95% CI 11.9-18.2) in those without AKI, p < 0.001. This is the first multinational cross-sectional study on the epidemiology of AKI in ICU patients using the complete KDIGO criteria. We found that AKI occurred in more than half of ICU patients. Increasing AKI severity was associated with increased mortality, and AKI patients had worse renal function at the time of hospital discharge. Adjusted risks for AKI and mortality were similar across different continents and regions.

Physical characteristics and occurrence rates of meteoric plasma layers detected in the Martian ionosphere by the Mars Global Surveyor Radio Science Experiment

Low‐altitude plasma layers are present in 71 of 5600 electron density profiles from the Martian ionosphere obtained by the Mars Global Surveyor Radio Science experiment. These layers are produced by the ablation of meteoroids and subsequent ionization of meteoric atoms. The mean altitude of the meteoric layer is 91.7 ± 4.8 km. The mean peak electron density in the meteoric layer is (1.33 ± 0.25) × 1010 m−3. The mean width of the meteoric layer is 10.3 ± 5.2 km. The occurrence rate of meteoric layers varies with season, solar zenith angle, and latitude. Seasonal variations in occurrence rate are particularly strong, often exceeding an order of magnitude. Meteoric layer altitude, peak electron density, and width are all positively correlated, with correlation coefficients of 0.3–0.4. Other correlation coefficients between the physical characteristics of meteoric layers and atmospheric or observational properties, such as scale height, solar zenith angle, and solar flux, have absolute values that are significantly smaller, indicating lack of correlation. The photochemical lifetime of plasma in meteoric layers is ∼12 days and depends on altitude.

Spatial and temporal variations in species occurrence rate affect the accuracy of occurrence models

ABSTRACTAim Predictive models of species occurrence have potential for prioritizing areas for competing land uses. Before widespread application, however, it is necessary to evaluate performance using independent data and effective accuracy measures. The objectives of this study were to (1) compare the effects of species occurrence rate on model accuracy, (2) assess the effects of spatial and temporal variation in occurrence rate on model accuracy, and (3) determine if the number of predictor variables affected model accuracy.Location We predicted the distributions of breeding birds in three adjacent mountain ranges in the Great Basin (Nevada, USA).Methods For each of 18 species, we developed separate models using five different data sets — one set for each of 2 years (to address the effects of temporal variation), and one set for each of three possible pairs of mountain ranges (to address the effects of spatial variation). We evaluated each model with an independent data set using four accuracy measures: discrimination ability [area under a receiver operating characteristic curve (AUC)], correct classification rate (CCR), proportion of presences correctly classified (sensitivity), and proportion of absences correctly classified (specificity).Results Discrimination ability was not affected by occurrence rate, whereas the other three accuracy measures were significantly affected. CCR, sensitivity and specificity were affected by species occurrence rate in the evaluation data sets to a greater extent than in the model‐building data sets. Discrimination ability was the only accuracy measure affected by the number of variables in a model.Main conclusions Temporal variation in species occurrence appeared to have a greater impact than did spatial variation. When temporal variation in species distributions is great, the relative costs of omission and commission errors should be assessed and long‐term census data should be examined before using predictive models of occurrence in a management setting.

Geographical variation in rate of schizophrenia in rural Ireland by place at birth vs place at onset

This study examined geographical variation in rate of occurrence of schizophrenia by place at birth vs place at onset, among a rural Irish catchment area population of unusual stability and socioeconomic homogeneity. Within a catchment area of 21 520 persons, all cases of schizophrenia were sought using current inpatient and outpatient records and key informants active in the community. Suspected cases were interviewed personally and diagnosed using DSM-III-R criteria. Place at birth and place at onset of psychosis were specified among the 32 District Electoral Divisions constituting the study region. For the 72 cases ascertained, an unremarkable overall prevalence rate/morbid risk obscured substantial and significant geographical variations therein between District Electoral Divisions. Particularly after controlling for high-density families, men demonstrated prominent geographical variation both by place at birth and by place at onset, with most men remaining unmarried and becoming ill at their place of birth; conversely, women demonstrated prominent variation by place at birth but more limited variation by place at onset, despite more frequent transitions from the parental home to the marital home before onset. Even when cases changed their location before the onset of psychosis, geographical variation in rate of occurrence of schizophrenia remained associated more strongly with factors related to the place of their birth.

A statistical study of MHD discontinuities in the inner solar system: Helios 1 and 2

A statistical study is made of the magnetic field directional discontinuities observed in early 1976 onboard Helios 1 and 2. Strong day-to-day variations of occurrence rates are found on either tangential (TD) or rotational (RD) discontinuities. No large variation (if any) is found versus either heliocentric distance or heliographic latitude. This contradicts previous findings obtained by the same technique on Pioneer 8 data in 1968–69; however, reasons are given to expect different results, under different solar conditions. The most interesting results come from the study of the morphology of discontinuities: first of all, the orientation of TD's and RD's normals (identified by a minimum variance technique) are strongly organized by the average magnetic field, following their progressive directional change when approaching the Sun. The inclination (θ n ) and azimuthal (ϕ n ) distributions are gaussian and strongly peaked along the field lines for RD's; as regards TD's the normals are perpendicular to the average field and follow its progressive variation; the θ n distribution is isotropic in solid angle, which is interpreted as evidence of crossing of flux tubes on the order of one/hour. Implications of this interpretation in contrast with a turbulent approach are also discussed.

Two earthquake swarms on the Kermadec Ridge

Abstract Two earthquake swarms on the Kermadec Ridge, in April 1961 and January 1965, occurred in almost the same place, roughly 4° from the North Island coast. New Zealand seismograph stations recorded about 200 events of magnitude M L ≥ 4 in each swarm. The first swarm lasted 2.3 days and the second 13.5 days. The average values of b are: 1.50 ± 0.19 and 1.34 ± 0.20, respectively. The frequency-magnitude relation varied during the course of the two swarms, but the patterns of changes are different. In the 1961 swarm, the variation in rate of occurrence has two stages, one similar to that in a foreshock sequence, and one like that in an aftershock sequence; the 1965 swarm followed the pattern typical of aftershocks.