892 resultados para Coverage bias


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Este trabajo comparó la cobertura de revistas procedentes de América Latina y el Caribe incluidas en SciELO, RedALyC y SCOPUS, por país y por tema. Calculó el porcentaje de revistas en estas fuentes en relación con las registradas en el catálogo de LATINDEX. Estimó el volumen de la producción científica que registra visibilidad en las tres fuentes y su evolución en el período 2005-2009. Los resultados indicaron que las tres fuentes son complementarias. En promedio, el porcentaje de solapamiento de títulos es bajo y desigual la distribución de revistas por países. Ningún país registró en las fuentes estudiadas todas las revistas incluidas en LATINDEX. SCOPUS y SciELO están más equilibradas temáticamente que RedALyC, que mostró un marcado sesgo hacia las ciencias sociales. El volumen de producción científica visible en SCOPUS es muy superior al de SciELO y RedALyC, aunque su distribución por países es muy desigual. Las tres fuentes registran tendencias de crecimiento de la producción en el período analizado

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Este trabajo comparó la cobertura de revistas procedentes de América Latina y el Caribe incluidas en SciELO, RedALyC y SCOPUS, por país y por tema. Calculó el porcentaje de revistas en estas fuentes en relación con las registradas en el catálogo de LATINDEX. Estimó el volumen de la producción científica que registra visibilidad en las tres fuentes y su evolución en el período 2005-2009. Los resultados indicaron que las tres fuentes son complementarias. En promedio, el porcentaje de solapamiento de títulos es bajo y desigual la distribución de revistas por países. Ningún país registró en las fuentes estudiadas todas las revistas incluidas en LATINDEX. SCOPUS y SciELO están más equilibradas temáticamente que RedALyC, que mostró un marcado sesgo hacia las ciencias sociales. El volumen de producción científica visible en SCOPUS es muy superior al de SciELO y RedALyC, aunque su distribución por países es muy desigual. Las tres fuentes registran tendencias de crecimiento de la producción en el período analizado

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The operator effect is a well-known methodological bias already quantified in some taphonomic studies. However, the replicability effect, i.e., the use of taphonomic attributes as a replicable scientific method, has not been taken into account to the present. Here, we quantified for the first time this replicability bias using different multivariate statistical techniques, testing if the operator effect is related to the replicability effect. We analyzed the results reported by 15 operators working on the same dataset. Each operator analyzed 30 biological remains (bivalve shells) from five different sites, considering the attributes fragmentation, edge rounding, corrasion, bioerosion and secondary color. The operator effect followed the same pattern reported in previous studies, characterized by a worse correspondence for those attributes having more than two levels of damage categories. However, the effect did not appear to have relation with the replicability effect, because nearly all operators found differences among sites. Despite the binary attribute bioerosion exhibited 83% of correspondence among operators it was the taphonomic attributes that showed the highest dispersion among operators (28%). Therefore, we conclude that binary attributes (despite showing a reduction of the operator effect) diminish replicability, resulting in different interpretations of concordant data. We found that a variance value of nearly 8% among operators, was enough to generate a different taphonomic interpretation, in a Q-mode cluster analysis. The results reported here showed that the statistical method employed influences the level of replicability and comparability of a study and that the availability of results may be a valid alternative to reduce bias.

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Aerial surveys of narwhals (Monodon monoceros) were conducted in the Canadian High Arctic during the month of August from 2002 to 2004. The surveys covered the waters of Barrow Strait, Prince Regent Inlet, the Gulf of Boothia, Admiralty Inlet, Eclipse Sound, and the eastern coast of Baffin Island, using systematic sampling methods. Fiords were flown along a single transect down the middle. Near-surface population estimates increased by 1.9%-8.7% when corrected for perception bias. The estimates were further increased by a factor of approximately 3, to account for individuals not seen because they were diving when the survey plane flew over (availability bias). These corrections resulted in estimates of 27 656 (SE = 14 939) for the Prince Regent and Gulf of Boothia area, 20 225 (SE = 7285) for the Eclipse Sound area, and 10 073 (SE = 3123) for the East Baffin Island fiord area. The estimate for the Admiralty Inlet area was 5362 (SE = 2681) but is thought to be biased. Surveys could not be done in other known areas of occupation, such as the waters of the Cumberland Peninsula of East Baffin, and channels farther west of the areas surveyed (Peel Sound, Viscount Melville Sound, Smith Sound and Jones Sound, and other channels of the Canadian Arctic archipelago). Despite these probable biases and the incomplete coverage, results of these surveys show that the summering range of narwhals in the Canadian High Arctic is vast. If narwhals are philopatric to their summering areas, as they appear to be, the total population of that range could number more than 60 000 animals. The largest numbers are in the western portion of their summer range, around Somerset Island, and also in the Eclipse Sound area. However, these survey estimates have large variances due to narwhal aggregation in some parts of the surveyed areas.