The Quarterly National Accounts in real-time: an analysis of the revisions over the last decade
In this article, the revisions of the Portuguese Quarterly National Accounts over the last decade are analyzed. We assess the real-time behaviour of GDP estimates and corresponding expenditure and supply side components. In particular, we focus on the revisions up to one year after the release of the fi rst estimate as well as on the revisions resulting from the inclusion of the Annual National Accounts. In the case of GDP, the reliability of the fl ash estimate, more recently made available by INE, is also assessed. The results for GDP suggest that the revisions up to one year are not signifi cant although the revisions can be larger when the Annual National Accounts are included. The expenditure components related with external trade present the largest revisions while the supply side estimates are more fragile than those from the expenditure side.
News and Noise in G-7 GDP Announcements
Revisions to GDP announcements are known to be quite large in all G-7 countries; quarterly growth rate revisions are regularly more than a full percentage point at an annualized rate. We examine the predictability of these revisions using standard statistical tests of whether the preliminary announcement is a rational forecast of the subsequently revised data. Previous work suggests that U.S. GDP revisions are largely unpredictable, as would be the case if the revisions reflect news not available at the time that the preliminary number is produced.We find that the degree of predictability varies throughout the G-7. Although we find little predictability in U.S. revisions, the data revisions for several foreign countries are highly predictable. We also perform a simple real-time forecasting exercise showing that for several countries, the predictability of data revision could be used to generate improved preliminary data.
Size-selective neuronal changes in the anterior optic pathways suggest a differential susceptibility to injury in multiple sclerosis.
Axonal damage is found in both acute and chronic lesions of multiple sclerosis. Direct axon counting in post-mortem tissue has suggested that smaller axons might have a greater susceptibility to damage, but methodological limitations have precluded unequivocal interpretation. However, as neuronal and axonal sizes are linked and neuronal changes would be expected with retrograde or transsynaptic degeneration following axon injury, we hypothesized that an alternative strategy for studying this phenomenon would be to define multiple sclerosis-associated changes in neurones. To test this hypothesis, we measured both axonal loss and neuronal size changes in the anterior optic pathway [including the optic nerve (ON), optic tract (OT) and lateral geniculate nucleus] of the brains of eight patients who died with multiple sclerosis and in eight control brains. The ONs and OTs in brains from the multiple sclerosis patients showed a trend to smaller mean cross-sectional areas (ON, multiple sclerosis = 6.84 mm(2), controls = 9.25 mm(2); and OT, multiple sclerosis = 6.45 mm(2), controls = 7.94 mm(2), P = 0.08) and had reduced axonal densities (ON, multiple sclerosis = 1.1 x 10(5)/mm(2), controls = 1.7 x 10(5)/mm(2); and OT, multiple sclerosis = 1.4 x 10(5)/mm(2), controls = 1.8 x 10(5)/mm(2), P = 0.006). Estimated total axonal counts were reduced by 32 (OT)-45% (ON) in the patients relative to controls (ON, multiple sclerosis = 8.1 x 10(5) axons, controls = 14.8 x10(5), P = 0.05; and OT, multiple sclerosis = 9.1 x 10(5), controls = 13.3 x 10(5), P = 0.02). The size distributions of the magnocellular cells in the lateral geniculate nucleus were similar for the two groups, but in multiple sclerosis brains the parvocellular cells were significantly smaller (mean sizes: multiple sclerosis = 226 microm(2), controls = 230 microm(2), P < 0.001) and had a larger variation in size, suggesting a greater proportion of atrophic neurones. Axon loss in the optic nerves of multiple sclerosis patients correlated strongly with measures of increased dispersion of cell sizes in the parvocellular layer (r = 0.8, P < 0.04). These data demonstrate that both atrophy and decreased density contribute to the substantial axonal loss in the anterior visual pathway of these patients. This appears related to a relatively selective atrophy of the smaller neurones of the parvocellular layer in the lateral geniculate nucleus, supporting the hypothesis that smaller axons may be preferentially susceptible to injury in multiple sclerosis.