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Evidenze relative alla Malaria in Europa (1999 – 2009). Igiene e Sanità Pubblica, 2010;3(S1):459
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Evidenze relative alla Malaria in Europa (1999 – 2009). Igiene e Sanità Pubblica, 2010;3(S1):459
No full textSynthesis, stability, and release processes of submicron vaterite containers in biological media
No full textInvestigating the level of significance of the coherence function in cardiovascular variability analysis
No full textAlthough the presence of significant coupling between cardiovascular variability series is usually verified according to the threshold value of 0.5 in the coherence function (CF), parameters of spectral estimator should be considered. In this study the surrogate data technique was introduced to define the level of significance of CF. The proposed method determined a frequency-dependent threshold over which the hypothesis of zero coherence was rejected. The weighted covariance method and the autoregressive method were used to estimate CF on simulated series with different degrees of linear coupling and on real cardiovascular data. The threshold was dependent on the type and parameters of the adopted coherence estimator and on the record length, demonstrating the applicability of the method for all types of spectral estimator. This should favor its introduction for assessing the reliability of transfer function estimates in cardiovascular variability analysis
Experimental approach for testing the uncoupling between cardiovascular variability series
No full textIn cardiovascular variability analysis, the significance of the coupling between two series is commonly assessed by defining a zero level on the magnitude-squared coherence (MSC). Although the use of the conventional value of 0.5 does not consider the dependence of MSC estimates on the analysis parameters, a theoretical threshold Ttis available only for the weighted covariance (WC) estimator. In this study, an experimental threshold for zero coherence Tewas derived by a statistical test from the sampling distribution of MSC estimated on completely uncoupled time series. MSC was estimated by the WC method (Parzen window, spectral bandwidth B = 0.015, 0.02, 0.025, 0.03 Hz) and by the parametric autoregressive (AR) method (model order M = 4, 8, 12, 16), on time series with length L = 180, 300, 420, 540 s. Tedecreased with increasing B and L and with decreasing M (range: 0.11-0.54 for WC estimator, 0.06-0.46 for AR estimator). Values for the typical parameter settings of WC and AR estimation (B = 0.025 Hz;- M = 8; L = 300 s) were, respectively, 0.24 and 0.17. Moreover, Ttwas always higher (range: 0.12-0.65) and the results were less dependable than those for Tein defining the zero level of MSC. Thus, with the proposed method, the hypothesis of uncoupling is rejected by accounting for the parameters that affect the confidence of spectral and cross-spectral estimates. The broad applicability of this approach should favour its introduction for assessing the significance of the coupling between cardiovascular variability series
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