9,117 research outputs found
Out-of-sample comparison of copula specifications in multivariate density forecasts
We introduce a statistical test for comparing the predictive accuracy of competing copula specifications in multivariate density forecasts, based on the Kullback-Leibler Information Criterion (KLIC). The test is valid under general conditions: in particular it allows for parameter estimation uncertainty and for the copulas to be nested or non-nested. Monte Carlo simulations demonstrate that the proposed test has satisfactory size and power properties in finite samples. Applying the test to daily exchange rate returns of several major currencies against the US dollar we find that the Student's t copula is favored over Gaussian, Gumbel and Clayton copulas. This suggests that these exchange rate returns are characterized by symmetric tail dependence.
Partial Likelihood-Based Scoring Rules for Evaluating Density Forecasts in Tails
We propose new scoring rules based on partial likelihood for assessing the relative out-of-sample predictive accuracy of competing density forecasts over a specific region of interest, such as the left tail in financial risk management. By construction, existing scoring rules based on weighted likelihood or censored normal likelihood favor density forecasts with more probability mass in the given region, rendering predictive accuracy tests biased towards such densities. Our novel partial likelihood-based scoring rules do not suffer from this problem, as illustrated by means of Monte Carlo simulations and an empirical application to daily S\&P 500 index returns.
Cooperating if oneĆ¢ā¬ā¢s Goals are Collective-Based: Social Identification Effects in Social Dilemmas as a Function of Goal-Transformation
Prior studies of the effect of group identification on cooperation in social dilemmas have advanced two competing accounts of this effect, the goal-transformation hypothesis, which holds that identification implies a sense of collective self, which makes personal and collective goals interchangeable, and the goal-amplification hypothesis, which states that identification induces positive expectations about othersĆ¢ā¬ā¢ cooperative behavior. These prior studies have, however, neglected to assess the process measures necessary to pit the one account against the other. Following prior research, the present study showed that the effect of identification was moderated by participantsĆ¢ā¬ā¢ social value orientation (i.e., individual differences in evaluating the importance of outcomes for self and other) in such a way that identification influenced proselfsĆ¢ā¬ā¢ cooperation more than prosocialsĆ¢ā¬ā¢ cooperation. This suggests that the consequence of group identification is that collective goals become personal goals. Extending earlier recent research, mediational analyses showed that the effect of our identification manipulation was mediated by participantsĆ¢ā¬ā¢ sense of collective self and not by their expectations. Taken together, these results provide strong support in favor of the goal-transformation hypothesis.Goal-amplification hypothesis;Goal-transformation hypothesis
Trackways in the Stormberg
Main articleVertebrate trackways in the lower groups of the
Karoo Supergroup are mainly pre- Beaufort fish
trails, although some tetrapod trackways are known
(Griffiths, 1963, p. 292; plate I; specimens in the
South African Museum). Recently fish trails have
been discovered in the Beaufort, for instance at Kilburn
and Wagondrift, but the Beaufort, despite its
rich amphibian, reptilian and synapsid fauna, is remarkable
for the paucity of its vertebrate trackways.
Of the Stormberg (of Lesotho) it was early noted
"Fossils are comparatively rare, but reptile tracks
are fairly abundant"Non
Insect faunas of South Africa from the upper permian and the Permian/Triassic boundary
Main articleThose sites in South Africa where more than one insect fossil specimen has been found have been
interpreted as younger than Middle Triassic or as Late Permian. One site which has yielded a number
of specimens and is apparently near the Permian/Triassic boundary is a quarry in the town of Bulwer
KwaZulu-Natai. There are six sites with more than one insect specimen which are stratigraphically lower
than Bulwer, namely Escourt (a new site), Far End, Mooi River (National Road), Mount West,
Balgowan and Lidgetton. According to the 1984 1: 1 000 000 Geological Map of South em Africa Bulwer
is situated in the Tarkastad Subgroup of the Beaufort Group near its lower boundary; the Tarkastad has
been considered as Triassic. The remaining sites, except Balgowan and Lidgetton, fall in the Estcourt
Formation of the Beaufort Group, as do all the sites with single Late Permian specimens except for one
similarly aged specimen from the more easterly Emakwezeni Formation. The stratigraphically lowest
sites are Lidgetton and slightly younger Balgowan; both are mapped as VoIksrust Formation of the Ecca
Group. An analysis is made of vertical distribution of taxa, with those of Lidgetton and Balgowan
grouped together as a lower unit, of Bulwer as upper unit, and of the Estcourt Formation sites and
Emakwezini site as a middle unit. No obvious break between the three units has been noted.Non
African fossil Lissamphibia
Main articleThe Anura (Frogs and Toads) are represented in Africa and associated regions by fossils of
every epoch from the Cretaceous to the Holocene. Pipid frogs of African affinity are known from
the Early Cretaceous of Israel and Later Cretaceous of South America and Africa; those of Israel
and South America have been well-studied, but only one from Africa has been: Eoxenopoides
reuningi from Namaqualand. Two well-studied Palaeocene frogs of South America, Shelania
pascuali and Xenopus romeri, have affinities with the African pipids. Apart from a Miocene
assemblage from North Africa (including pipids, which are now exclusively sub-Saharan) and one
species from Namibia, Xenopus stromeri, the fossil African anurans remain largely unstudied.
Deposits in which the African anuran fossils occur represent crater lakes, other lacustrine deposits,
including lacustrine tuffs, river terraces, deltas, estuarine/lagoon zones, karst landscapes and
archaeological sites; data are not available for several of the recorded fossils. No fossils in Africa
appear to have been definitely ascribed to the Urodela or Caecilia.Non
Where to go in the near future: diverging perspectives on online public service delivery
Although the electronic government is under heavy development, a clear vision doesnāt seem to exist. In this study 20 interviews among leaders in the field of e-government in the Netherlands resulted in different perspectives on the future of electronic public service delivery. The interviews revealed different objectives and interpretations of the presuppositions regarding citizensā desires. Opinions about channel approaches and ātrigger servicesā appeared to vary. Furthermore, the respondents didnāt agree on the number of contact moments between citizen and government, had different opinions about digital skills, pled for various designs of the electronic government and placed the responsibility for electronic service delivery in different hands. Conclusion is that there is a lack of concepts on how to do things. Everybody talks about eGovernment, but all have different interpretations. \u
Are the orthostatic fluid shifts to the calves augmented in autonomic failure?
In autonomic failure (AF), blood pressure (BP) falls upon standing which is commonly ascribed to defective vasoconstriction and excessive pooling. Observations on the amount of pooling in AF are contradictory. We evaluated pooling using strain-gauge plethysmography (SGP) during head-up tilt (HUT) with a parachute harness fixed to the tilt table to avoid muscle tension in the lower limbs and thus to maximise pooling. 23 healthy subjects and 12 patients with AF were tilted for 5 min. BP and calf volume changes, as measured by SGP, were measured continuously. Multiple regression analysis was used to examine the effect of AF on orthostatic fluid shifts after adjustment for potential confounders. Patients did not differ from controls with respect to the increase of calf volume after 5 min HUT. The acute (0-1 min) and the prolonged (1-5 min) phases of calf volume responses to HUT were also similar between patients and controls. No correlation was found between the degree of orthostatic hypotension and the orthostatic calf volume change in AF. In one patient an additional measurement was made before rising from bed in the early morning demonstrating a greater albeit small increase of calf volume upon HUT. Orthostatic fluid shifts at the level of the calf in AF are not augmented during the course of the day despite marked hypotension. However, a small increase of pooling may be expected when the patient first gets out of bed in the morning probably due to the absence of oedema.Paroxysmal Cerebral Disorder
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